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<\/a><\/p>\nIf you bounce a significant number of messages, keep sending emails to an address that bounced, and\/or repeatedly send email campaigns with bounces, you\u2019re sending a signal to the email service providers and email clients you\u2019re sending spam<\/strong>. (Or, at the very least, you\u2019re not sending individual messages that people actually want.)<\/p>\n That can have a serious impact on your deliverability.<\/p>\n In this article, we\u2019ll cover everything you need to know about email bounce codes<\/strong>: What they are, how they\u2019re determined, a list of the common (and not-so-common) bounce codes you might encounter, how to handle bounced emails, and ways to cut down on bounces.<\/p>\n Bounce codes are messages from a mail server to indicate why an email you sent was not able to be delivered.<\/p>\n Bounce codes indicate whether the failure was a \u201csoft bounce\u201d (meaning a temporary problem) or a \u201chard bounce\u201d (meaning a permanent problem).<\/p>\n The codes also shed light on the specific problem<\/b>, which can range from the user having a full mailbox to an email account that no longer exists.<\/p>\n Soft bounces are emails that bounce for a temporary reason. For instance, the recipient\u2019s mailbox might be full or there might\u2019ve been an error with their mail server.<\/p>\n Hard bounces are emails that bounce for a permanent reason. For instance, the recipient\u2019s mailbox no longer exists.<\/p>\n The general rule of thumb is to retry sending to addresses that soft bounce<\/b> \u2014 and to stop trying to send to addresses that hard bounce <\/b>on this campaign and in the future.<\/p>\n Your email service provider may handle bounce management<\/a> for you. (For instance, at GMass, we automatically suppress your future messages to email addresses that have hard bounced.)<\/p>\n If not, you\u2019ll want to manually remove those addresses from your list<\/b>, as hard bounces are a major red flag to the email clients and can affect your deliverability.<\/p>\n Traditional SMTP bounce codes are three-digit numbers (e.g., 554) which indicate an email\u2019s successful or unsuccessful delivery. If that delivery is unsuccessful, the codes give you insight into why they were unsuccessful.<\/p>\n For example, the status code Codes that start with a 4 (e.g., The idea for enhanced SMTP bounce codes<\/a> came about in 2003 as a way to more completely describe a mail system error. The group that proposed the enhanced codes wrote, \u201cSMTP provides about 12 useful codes for delivery reports\u2026 each of the 12 useful codes are overloaded to indicate several error conditions.\u201d<\/p>\n So enhanced bounce codes include three separate digits, separated by periods, which allows the bounce notifications to give more specific detail into why message delivery failed<\/b>.<\/p>\n In the three-number enhanced codes, the first digit is the delivery class, where:<\/p>\n The second digit indicates where in the process things went wrong. For instance, in And the third digit gives even more detail about the specific issue. For instance, 5.1.1 means there was a bad destination mailbox address (in an name@domain.com email, \u201cname\u201d was invalid).<\/p>\n So will you receive traditional bounce codes or enhanced ones when you send your messages? Today, you\u2019ll largely see a combination of the two<\/b>.<\/p>\n For instance, Google uses the traditional three-digit code to give a general overview of the issue, then uses the three-number enhanced code to elaborate.<\/p>\n In our glossary, we\u2019ll mostly cover this modern format: Bounce notifications that combine the three-digit traditional reply codes with the three-number enhanced status codes.<\/p>\n Here\u2019s your guide to some of the most common email bounce codes you may encounter and what they mean.<\/p>\n These are soft bounce codes, generally indicating a temporary issue with the recipient\u2019s mail server or mailbox. You can safely try to resend your messages to addresses that give you these bounce codes<\/p>\n This is a precarious bounce message \u2014 and a sign you should slow down on mass email<\/a> and cold email<\/a> campaigns until Google trusts you again.<\/p>\n As a spam prevention measure, most of the major email clients cap how many emails a person can receive over a certain time frame. For instance, Google caps Gmail users at receiving 60 emails per minute, 3,600 per hour, or 86,400 per day.<\/p>\n Keep an eye on this address. It\u2019s possible that even though the account still exists, the person isn\u2019t monitoring the mailbox anymore. So while this is a soft bounce, if you continue to get soft bounces on messages to this recipient, you should probably remove them from your list.<\/p>\n This error indicates you\u2019ve exceeded your daily sending limits with Gmail. (Which are up to 500 emails per day for a free Gmail account and up to 2,000 emails per day for a paid Google Workspace account.)<\/p>\n We\u2019ve covered Gmail limits extensively here at GMass \u2014 because we\u2019re one of the only Gmail-based email services that allows you to break through those limits<\/a>. Here\u2019s more about how to send virtually unlimited emails through Gmail<\/a>.<\/p>\n These are some of the more common hard bounce codes you\u2019ll receive.<\/p>\n A good general rule of thumb is to remove addresses from your email list immediately. Yes, there might be a few addresses that ultimately would work down the road \u2014 but most won\u2019t. And if you keep on sending to addresses that hard bounce it\u2019s a big indication to the email services that you\u2019re sending spam.<\/p>\n These codes are often typo-related (or because you copied and pasted an email that contained invalid characters). You\u2019ll need to fix the errors in the address before you can send the email.<\/p>\n Your address may appear on a blacklist or your message may have spam indicators, so the external server rejected it. Make sure your emails aren\u2019t mistaken for spam (you can see strategies for that later in this article).<\/p>\n You can also use this email analyzer tool<\/a> to find out if you\u2019re on any of the common spam blacklists.<\/p>\n While this error may<\/i> mean a recipient deleted their email address, this error is also frequently caused by human error. Like… did you mean to send to bill@microsoft.com and not biil@microsoft.com?<\/p>\n This is another case where a typo might be at fault. Is the domain name wrong in your list? Or maybe an extra character like a \/ or a , snuck in there?<\/p>\n While this is a hard bounce code, it\u2019s similar to the soft bounce for a mailbox that\u2019s receiving too many messages. You can try this address again safely in the future.<\/p>\n But\u2026 if someone is really<\/i> receiving emails at a rate of one-per-second or higher, is your message going to be able to cut through that noise?<\/p>\n This is an issue on your end \u2014 did you try to test the limits to see just how many people you could put into the To field<\/a>?<\/p>\n This error indicates a problem on your end, not the recipient\u2019s. Check your account and server configuration.<\/p>\n This bounce warning is, essentially, Google telling you they think you\u2019re sending spam. It\u2019s time to try to save the email address by stopping mass and cold email campaigns and sending individual emails for a bit.<\/p>\n This bounce could mean your message didn\u2019t pass the recipient\u2019s language filters. Which is why we suggest dropping no more than six f-bombs per cold email. (Joke! That\u2019s a joke! The right answer is zero. Now and always.)<\/p>\n So while it\u2019s a hard bounce code, you can try sending to the address again in the future \u2014 with more careful attention toward spam-triggering words you might be using.<\/p>\n If you receive any of these bounce messages you need to look into your SPF, DKIM, and DMARC records. One good way: Send a test email to this Email Analyzer<\/a>. It will show you the entire technical \u201cconversation\u201d of your messages. And if it spots any issues with your authentication records, you\u2019ll know what you need to fix.<\/p>\n You can try resending to these This is another hard bounce that may be caused by a typo.<\/p>\n Mimecast has blocked your message \u2014 here are some tips for getting around Mimecast blocks<\/a>.<\/p>\n These cryptographic-related codes often correspond to encrypted messages \u2014 especially ones that are too<\/i> encrypted.<\/p>\n Most modern email service providers have some degree of bounce management built in<\/b>, meaning they\u2019ll respond to a hard bounce one of these ways:<\/p>\n And with soft bounces, many email service providers will try to resend a few times to the address.<\/p>\n All of this is a good blanket approach to bounces.<\/p>\n The goal is two-fold. One, to keep you from sending repeated messages to addresses that hard bounce<\/b>, which can have a negative effect on your sender reputation. And two, to cut down on the manual list hygiene and maintenance<\/b> work on your end.<\/p>\n As you evaluate email providers, keep an eye out for their bounce management.<\/p>\n At GMass, for example, we suppress future emails to addresses that hard bounce<\/a> (although we will<\/i> let you override that and send away if you want).<\/p>\n You can also manage bounced addresses<\/a> and remove emails from the list.<\/p>\n We\u2019ve also created a few other cool bounce management features to help keep bounces from have any sort of negative effect.<\/p>\n With global bounces<\/a> enabled, GMass will check the bounce lists of everyone using the same sending domain as you (e.g., @mycompany.com) as well as everyone on your GMass team plan \u2014 and it will suppress messages you send to addresses on any of those lists<\/b>. (This is also true for unsubscribes.)<\/p>\n And when you get a bounce notification email and open it \u2014 did you know that can count as an \u201copen\u201d for the original email? That\u2019s because the original message is included in the bounce notification, so when you open the notification, you trigger the open-detection pixel in the original.<\/p>\n So we created Tracker Blocker<\/a>, which prevents you from triggering opens on your own emails<\/a><\/b> \u2014 which bounce notifications being one of the<\/i> major times that happens.<\/p>\n Bounce management is helpful and it\u2019s good to know what bounce codes mean \u2014 but really, the goal of every email campaign is zero bounces<\/b>.<\/p>\n (Well, except for the emails I sent trying to intentionally bounce emails to get the screenshots for this article.)<\/i><\/p>\n So here are four ways you can cut down on bounces and try to keep your bounce rate right around zero.<\/p>\n One way to figure out if email addresses on your list are valid? Send the campaign and see what bounces.<\/p>\n A much better way to figure out if the email addresses on your list are valid? Test the addresses before you send.<\/b><\/p>\n There are lots of email verification services<\/a> out there, most of which are paid. GMass offers free email verification<\/a> to users as well; GMass can test every address in a campaign right before your email goes to that address<\/b>.<\/p>\n Planning to buy an email list<\/b>? Expect a lot of addresses on there to bounce. (There also might be spam traps on there \u2014 emails that won\u2019t bounce but that email providers use to identify spammers.)<\/p>\n You also may run into trouble if you\u2019re using questionable email mining tools<\/b> to dig up contact info for prospects.<\/p>\n And, of course, there\u2019s the human error element<\/b> we discussed in the list of bounce codes \u2014 it\u2019s incredibly easy to mistype an address in your spreadsheet.<\/p>\n The more effort you put into assembling, proofreading, and validating your list, the fewer bounces you should see.<\/p>\n And if you aren\u2019t sending frequent emails (say, at least once a month), there\u2019s a chance several addresses on your list will become invalid in between sends. That\u2019s one of the many reasons it\u2019s recommended to email your list with a more frequent cadence.<\/p>\n Google limits how many emails you can send<\/b> in a day: up to 500 per day for free Gmail accounts and up to 2,000 per day for paid Google Workspace accounts. Once you cross your daily limit, your emails start bouncing.<\/p>\n If you\u2019re using a tool to send your email campaigns through Gmail, make sure that tool has a plan in place for handling Google\u2019s limits<\/a>.<\/p>\n Some of the tools that send through Google will simply limit your daily sends to make sure they\u2019re well below any possible account limits.<\/p>\n A few other tools, like us here at GMass, don\u2019t want to limit you like that<\/strong>.<\/p>\n So we automatically start slowing down your send as it approaches Gmail\u2019s limit, making sure that as soon<\/i> as the first \u201cover the limit\u201d bounce comes in we either pause the campaign for 24 hours or switch to sending it via a Email Bounce Codes: Table of Contents<\/h2>\n
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What Are Email Bounce Codes?<\/h2>\n
Soft bounces vs. hard bounces<\/h3>\n
Enhanced SMTP bounce codes vs. traditional SMTP bounce codes<\/h3>\n
550<\/code> means a user\u2019s mailbox was invalid.<\/p>\n421<\/code>) usually indicate a soft bounce; codes that start with a 5 (e.g., 550<\/code>) indicate a hard bounce.<\/p>\n\n
2.X.X<\/code> means successful delivery.<\/li>\n4.X.X<\/code> means temporary delivery issues (mostly soft bounces).<\/li>\n5.X.X<\/code> means permanent issues (mostly hard bounces).<\/li>\n<\/ul>\nX.1.X<\/code>, the 1 means there was an issue with the addressing. X.2.X<\/code> is a mailbox issue. X.3.X<\/code> is a mail system issue.<\/p>\nGlossary of Email Bounce Codes<\/h2>\n
Soft bounce codes (
4XX<\/code> and 4.X.X<\/code>)<\/h3>\n421 4.3.0 Temporary system problem. Try again later.<\/code><\/p>\n421 4.4.2 Network connection timed out.<\/code><\/p>\n421 4.4.5 Server busy, try again later.<\/code><\/p>\n421 4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address.<\/code><\/p>\n421 4.7.0 Try again later, closing connection.<\/code><\/p>\n422 4.2.2 The email account is over quota.<\/code><\/p>\n441 4.4.1 Error encountered while communicating with primary target IP address.<\/code><\/p>\n450 4.2.1 The user you are trying to contact is receiving mail too quickly.<\/code><\/p>\n450 4.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered.<\/code><\/p>\n450 4.2.1 Peak SMTP relay limit exceeded for customer.<\/code><\/p>\n451 4.3.0 Mail server temporarily rejected message.<\/code><\/p>\n451 4.3.0 Multiple destination domains per transaction is unsupported.<\/code><\/p>\n451 4.4.2 Timeout - closing connection<\/code><\/p>\n451 4.5.0 SMTP protocol violation.<\/code><\/p>\n452 4.2.2 The email account that you tried to reach is over quota.<\/code><\/p>\n452 4.5.3\u00a0 Domain policy size per transaction exceeded.<\/code><\/p>\n452 4.5.3 Your message has too many recipients.<\/code><\/p>\n454 4.5.0 SMTP protocol violation, no commands allowed to pipeline after STARTTLS.<\/code><\/p>\n454 4.7.0, Cannot authenticate due to temporary system problem.<\/code><\/p>\nHard bounce codes (
5XX<\/code> and 5.X.X<\/code>)<\/h3>\n500 5.0.0 Email address does not exist.<\/code><\/p>\n501 5.5.2 Cannot decode response.<\/code><\/p>\n501 5.5.4 HELO\/EHLO argument is invalid.<\/code><\/p>\n502 5.5.1 Too many unrecognized commands, goodbye.<\/code><\/p>\n502 5.5.1 Unimplemented command.<\/code><\/p>\n503 5.5.1 MAIL first.<\/code><\/p>\n503 5.5.1 RCPT first.<\/code><\/p>\n503 5.7.0 No identity changes permitted.<\/code><\/p>\n504 5.7.4 Unrecognized Authentication Type.<\/code><\/p>\n510 5.1.0 Other address status.<\/code><\/p>\n511 5.1.1 Bad email address.<\/code><\/p>\n513 5.1.3 Bad destination mailbox address syntax.<\/code><\/p>\n514 5.1.4 Destination mailbox address ambiguous.<\/code><\/p>\n516 5.1.6 Mailbox has moved.<\/code><\/p>\n517 5.1.7 Bad sender\u2019s mailbox address syntax.<\/code><\/p>\n518 5.1.8 Bad sender\u2019s system address.<\/code><\/p>\n521 5.2.1 AOL will not accept deliverability of this message.<\/code><\/p>\n530 5.5.1 Authentication Required.<\/code><\/p>\n530 5.7.0 Must issue a STARTTLS command first.<\/code><\/p>\n535 5.5.4 Optional Argument not permitted for that AUTH mode.<\/code><\/p>\n535 5.7.1 Application-specific password required.<\/code><\/p>\n541 The message could not be delivered for policy reasons.<\/code><\/p>\n542 5.4.2 Bad connection.<\/code><\/p>\n543 5.4.3 Routing server failure.<\/code><\/p>\n544 5.4.4 Unable to route.<\/code><\/p>\n546 5.4.6 Routing loop detected.<\/code><\/p>\n547 5.4.7 Delivery time expired.<\/code><\/p>\n550 5.1.1 The email account that you tried to reach does not exist.<\/code><\/p>\n550 5.1.2 The domain name of the email address seems to be invalid.<\/code><\/p>\n550 5.2.1 The email account that you tried to reach is disabled.<\/code><\/p>\n550 5.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered.<\/code><\/p>\n550 5.4.5 Daily sending quota exceeded.<\/code><\/p>\n550, 5.4.5 Daily SMTP relay limit exceeded for user.<\/code><\/p>\n550 5.5.3 Too many recipients attached.<\/code><\/p>\n550 5.7.0 Mail relay denied.<\/code><\/p>\n550 5.7.0 Mail Sending denied.<\/code><\/p>\n550 5.7.1 Email quota exceeded.<\/code><\/p>\n550 5.7.1 Invalid credentials for relay.<\/code><\/p>\n550 5.7.1 Our system has detected that this message is likely unsolicited mail.<\/code><\/p>\n550 5.7.1 The user or domain that you are sending to (or from) has a policy that prohibited the mail that you sent.<\/code><\/p>\n550 5.7.1 Unauthenticated email is not accepted from this domain.<\/code><\/p>\n550 5.7.26 Unauthenticated email from domain-name is not accepted due to domain's DMARC policy.<\/code><\/p>\n550 5.7.26 This message does not have authentication information or fails to pass authentication checks (SPF or DKIM).<\/code><\/p>\n550 5.7.26 This message fails to pass SPF checks for an SPF record with a hard fail policy.<\/code><\/p>\n551 5.7.1. The message was rejected due to classification as virus, spam, or high bulk ratio.<\/code><\/p>\n552 5.2.2 This message is larger than the current system limit.<\/code><\/p>\n552 5.2.3 Your message exceeded Google's message size limits.<\/code><\/p>\n552<\/code> accounts with a smaller message (maybe one without an attachment). But if you were<\/i> sending a regular, mostly-text message and still got this code, it\u2019s an indication the mailbox is no longer attended.<\/p>\n553 5.1.2 We weren't able to find the recipient domain.<\/code><\/p>\n554 5.6.0 Mail message is malformed.<\/code><\/p>\n554 5.6.0 Message exceeded 50 hops, this may indicate a mail loop.<\/code><\/p>\n554 5.7.0 Too Many unauthenticated commands.<\/code><\/p>\n554 Email rejected due to security policies - https:\/\/community.mimecast.com\/docs\/DOC-1369#554<\/code><\/p>\n555 5.5.2 Syntax error.<\/code><\/p>\n560 5.6.0 Other or undefined media error.<\/code><\/p>\n561 5.6.1 Media not supported.<\/code><\/p>\n570 5.7.0 Other or undefined security status.<\/code><\/p>\n571 5.7.1 Delivery not authorized, message refused.<\/code><\/p>\n572 5.7.2 Mailing list expansion prohibited.<\/code><\/p>\n573 5.7.3 Security conversion required but not possible.<\/code><\/p>\n574 5.7.4 Security features not supported.<\/code><\/p>\n575 5.7.5 Cryptographic failure.<\/code><\/p>\n576 5.7.6 Cryptographic algorithm not supported.<\/code><\/p>\n577 5.7.7 Message integrity failure.<\/code><\/p>\nBounce Management: How to Handle Email Addresses That Bounce<\/h2>\n
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<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n4 Ways to Cut Down on Bounces<\/h2>\n
1. Validate emails before you send<\/h3>\n
<\/a><\/p>\n2. Be careful how you source your email list<\/h3>\n
3. Beware of Google sending limits<\/h3>\n