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What is the message size limit with Paubox?

Paubox enforces message size limits to ensure reliable delivery and maintain optimal performance across our email infrastructure. Understanding these limits helps prevent undeliverable messages and ensures that large attachments reach their recipients without being bounced.

How message size limits work

Paubox applies different size limits depending on which service you are using. If a message exceeds these limits, it will bounce back to the sender as an undeliverable message.

The maximum message size limits are:

  • Paubox Email Suite: 150 MB for both inbound and outbound messages

  • Paubox Email API: 50 MB for outbound messages

For customers using Microsoft 365, it is important to account for transcoding which can increase files sizes by 33%. To avoid delivery issues caused by this size inflation, we recommend keeping attachments to 100 MB or lower when sending through Microsoft 365.

Important: Google Workspace and Microsoft 365 may enforce their own internal attachment size limits that are lower than the Paubox maximum. Always verify the limits of your specific primary mail provider.