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Deliverability to t-online.de

Sending volume, opens, bounce responses, and block messages observed by GMass for email sent to t-online.de.

Emails sent 1,876,247 Messages represented in this domain dataset
Unique opens 271,520 Unique open events associated with those sends
Open rate 14.5% Across all available data for t-online.de

Sent vs. opens

Change the date range or chart style. Bounce and block sections below follow the same selected date range.

Date Sent Opens Open rate

Blocks from t-online.de

SMTP responses that generally indicate a valid address whose message was rejected.

No blocks during the specified time frame.

Bounces from t-online.de

SMTP responses that generally indicate an invalid or undeliverable email address.

Bounce code guide
512 bounce events · 12 response types
  • 550-5.1.1 user unknown 550 5.1.1 Unknown recipient. 462
  • 559 5.1.9 Missing, invalid or non-matching DKIM signature 32
  • aggressive-handler 5
  • 554 IP=51.79.193.107 - None/bad reputation. Ask your postmaster for help or to contact for reset. 5
  • action not taken: mailbox unavailable 550 For explanation visit https://postmaster.1und1.de/en/case?c=r1601&i=ip&v=194.25.134.85&r=1MjQYG-1wNpzf2jX8-00j3sz 1
  • X-Postfix; delivery temporarily suspended: host mx03.t-online.de refused to talk to me: 450 4.7.1 554 IP=23.83.223.121 - None/bad reputation. Ask your postmaster for help or to contact for reset. 1
  • X-Postfix; lost connection with mx01.t-online.de while receiving the initial server greeting 1
  • X-Postfix; Host or domain name not found. Name service error for name=andcool.de type=A: Host not found 1
  • The recipient server did not accept our requests to connect. For more information, go to https://support.google.com/mail/answer/7720 1
  • 550 5.2.1 Mailbox is disabled 1
  • 550- 550-Your IP: 74.125.228.171 550-Mailhost: mailin37.t-online.de 550-Timestamp: 2026-09-26T12Z 149288:-DB7FDF4C-3042340E/10/63756578959 550-Authenticator: 550- 550-Your message has been rejected due to spam or virus classification. 550-If you feel this is inapplicable, please report the above error codes 550-back to to help us fix possible misclassification. 550-We apologize for any inconvenience and thank you for your assistance! 550- 550-Die Annahme Ihrer Nachricht wurde abgelehnt, da sie a 1
  • 550- 550-Your IP: 74.125.228.80 550-Mailhost: mailin33.t-online.de 550-Timestamp: 2026-10-03T15Z 149288:-9DFF8F51-268CA657/10/63756578959 550-Authenticator: 550- 550-Your message has been rejected due to spam or virus classification. 550-If you feel this is inapplicable, please report the above error codes 550-back to to help us fix possible misclassification. 550-We apologize for any inconvenience and thank you for your assistance! 550- 550-Die Annahme Ihrer Nachricht wurde abgelehnt, da sie al 1

Methodology

Send and open statistics

Send and open statistics are updated daily. Every day, open statistics are refreshed for the previous 14 days because not every open happens on the same day an email is sent. Open-rate data remains tied to the emails actually sent on each particular day.

Bounces and blocks

Bounces and blocks update in real time. SMTP responses are de-personalized so similar responses can be grouped for analysis. GMass categorizes responses through internal human review: bounces generally indicate an invalid address, while blocks generally indicate a valid address whose message was rejected.

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