SMTP Error From SwiftMailer


Active member
Affected version
We use Amazon SES for our mail sending service. Generally functions fine, but we get tons of errors every day in our error log of this form:

Swift_TransportException: Email to <some email> from <some email> failed: Expected response code 250 but got code "451", with message "451 4.4.2 Timeout waiting for data from client. "

Found this previous bug report that claimed this issue (among others) was fixed, but we are running 2.2.9 right now and the issue persists:

It's also worth noting that Swiftmailer appears to be dead and unmaintained as of late last year:

Will XenForo be moving to a new mail provider soon and/or is there something that can be done to resolve these mail send errors?
I've had this issue come up on a number of sites using SES. Not 100% certain it's something that would be automatically fixed by switching the email library but they have confirmed they're switching to Symfony Mailer here with XenForo 2.3
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