Symptoms
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When sending an email in webmail, the operation fails with the following error message:
SMTP Error: Message size exceeds server limit
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Emails with large attachments (more than 10 MB) are not received. The sender receives the following email message about failed email delivery:
552 5.3.4 Message size exceeds fixed limit
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The following error message may appear in
/var/log/maillog:warning: queue file size limit exceeded
Cause
The size of the email exceeds the limit configured in Plesk at Tools & Settings > Mail Server Settings > Maximum message size.
Note: When adding an attachment, its size is automatically increased due to the encoding that is performed when forwarding an email. On average, the email is enlarged by approximately 35-40% of the original attachment size. For instance, if you set a limit of 10 MB and send an email with a 9 MB attachment, the email will be rejected.
Resolution
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Go to Tools & Settings > Mail Server Settings.
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Increase the Maximum message size value.
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Click OK to apply the changes.