Maximum Size Of Outgoing Emails

All mail servers limit the total size of emails (specifically the MIME text). Unfortunately there is no industry standard maximum size. So the maximum email size you can send via ThinkAutomation is based on both your smarthost (the mail server you use to send outgoing emails specified in your ThinkAutomation Server Settings) and the recipients mail server.

Some example maximums:
  • Gmail - 25mb
  • Office 365 - 20mb (up to 150mb)
  • Exchange Server - 10mb
  • Amazon SES - 10mb
  • SendGrid - 30mb

The size of attachments you can send will be lower. This is because attachments are converted to base64 text before being added to the MIME text. This is roughly double the size of the attachment file itself. The email body text also reduces the size. So if you have a 2mb plaintext body and the recipients mail server accepts 10mb MIME text then you can add an attachment of roughly 4mb.

There is no direct way to know the recipients end mail server. Some - like Gmail you can tell from the email address itself. Eg: [email protected] you will know its Gmail.

ThinkAutomation itself limits the total size of attachments in outgoing emails to 10mb (this has recently been increased to 25mb). This is the binary size - not the MIME text size.

However, if you want to send large attachments you should consider the possibility that the recipients mail server may reject the message.

A better way would be to upload the file to cloud storage (you can use the Cloud Storage action for this), and then include a link to it in the email, rather than adding the file as an attachment.

Creation date: 29/06/2023 08:14      Updated: 10/07/2023 07:21