GMass users using the email auto follow-up feature may have noticed that their auto follow-ups failed to send sometimes. Below is an explanation of when the issue surfaces and how we fixed it.
If the original email campaign, to which the auto follow-ups were assigned, was larger than 1 MB, either by volume of text, or by attachment(s) that were larger than 1 MB when MIME-encoded into email format, then all stages of the auto follow-up emails failed to send. The user would not be notified of the send failure.
The Cause of the Issue
The cause of this has to do with how GMass processes auto follow-up emails when it’s time to send them. GMass would create a temporary Draft in the user’s account that stored pertinent details of the auto follow-up campaign. Recently, however, we discovered that Gmail Drafts are limited to 1 MB in size when the Draft is created by the Gmail API. Drafts created in the Gmail web interface do not have this limitation. If GMass attempted to create a Draft greater than 1 MegaByte with the Gmail API, an error would be returned that looked like:
Request payload size exceeds the limit: 1048576 bytes. 
Message[Request payload size exceeds the limit: 1048576 bytes.] Location[ – ] Reason[badRequest] Domain[global]
GMass is no longer using a Gmail Draft as a means of storing email auto follow-up details, and is instead creating a temporary message, which can be seen under “All Mail”. This temporary message will only live in a user’s Gmail account for a few seconds. It is deleted when an auto follow-up stage is actually sent.
Now, when the auto follow-up is sent, if the original email had attachments, regardless of size, the auto follow-up email will also contain the attachment(s) from the original campaign.
If you were affected by this issue…
Contact our support team. With your approval, we can manually trigger a past auto follow-up that failed to send because of this issue.