Troubleshooting - Signature 365 - Symprex Knowledge Base

A signature is not applied to emails with large attachments

Why server-side signatures are skipped on emails with large attachments and the size limits involved.

Enable server-side signatures after an initial client-side-only Signature 365 setup.

Fix 550 5.1.8 bad outbound sender errors when Signature 365 mail flow is misconfigured.

Resolve 550 5.4.1 recipient address rejected errors, especially for public folders routed through Signature 365.

Fix 550 5.7.1 unable to relay errors caused by Signature 365 connector or certificate configuration.

Troubleshoot 552 5.3.4 header size errors when oversized headers block Signature 365 mail processing.

Overview of Signature 365 server-side non-delivery report errors, linked fixes, and configuration-related causes.

Remove Signature 365 mailflow rules and Exchange Online connectors in the correct order.

Fix Digital Guardian x-dg headers causing 552 5.3.4 errors with Signature 365 server-side injection.

Generate a detailed debug log for the Signature 365 Transport Agent.

Fix add-in connection errors when using Signature 365 with on-premises mailboxes.

Using Signature 365 with read only access to Microsoft 365

Set up Signature 365 in read-only mode when you cannot create external connectors in Microsoft 365.

A signature is not applied to emails with large attachments

Why server-side signatures are skipped on emails with large attachments and the size limits involved.