You are using Exclaimer, and you notice that the emails with large attachments do not have a server-side signature appended to them.
To ensure that all emails are processed efficiently, it is necessary to impose a limit on the email size to which Exclaimer will add a server-side signature.
During transport, emails undergo some level of decompression, and emails can increase in size by up to 30%, depending on the content of the email. In worst-case scenarios, signatures may not be applied to emails having around 24MB (at the time of sending).
We recommend applying client-side signatures to emails with large attachments.
Options to connect to Microsoft 365
How to setup a Microsoft 365 subscription to use client-side signatures
How to setup a Microsoft 365 subscription to use server-side signatures