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Prolateral offers primary and backup domain (DNS) services, with servers in key geographic locations providing the best service possible.


What are the outmail message size limits?
What is a max size of a message?


outMail message size limit is set to 50Mb (MIME encode).

So what does that mean to an actual message size (to save me working out the MIME encoded size)?

Typically MIME encoding a message adds approx 36% to the real size of the message.  So a 50Mb MIME encoded message would be a real message of 36Mb in size.

Remember the MIME Message size will include the combined size of the headers, message body and all the attachments.


Q - Can the message limit be increased?
A - Yes but No. We could change the message limit size however if the receiving server has a smaller size limit the message would fail.

Q - Why 50Mb?
A - Original size limits were defined in the SMTP RFC Standards however when it became possible to attach multimedia to emails the attachment size grew, however please be aware that some ISP's still use 25Mb for their own message limits.

Q - My Exchange server won't let me send emails that large.
A - Check your message limits on the Send Connector it could be set to 10Mb by default.

Q - What are other ISPs message size limits?
A - Google Mail (GMail), BT, Yahoo Mail, AOL, VirginMedia are set to 25Mb. and Hotmail are set to 10Mb, however Office365 is 100Mb.

Q - Can I send a 100Mb to Office365 users?
A - No, see above the max message is 50Mb MIME encoded, You would need to compress and/or split your attachments.

Additional Information

For more information on message size limits, minimums and restrictions please refer to SMTP RFC (RFC 2821),


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