M365 - Why are some emails not sent immediately?

Created by Ben Hayes, Modified on Fri, 16 Jan at 3:13 PM by Ben Hayes

Microsoft 365 Mailbox

Sending emails via M365 Mailboxes (through MS Graph APIs) can experience failures from time to time. This can be for a series of reasons. For any issues where emails are being sent the following day to the rule, and where there is a M365 mailbox only, this is because the email has failed to send initially. This is how the system works to deal with these emails:

Automatic Retry for Failed Emails:

If an email fails to send, there is nightly scheduler that will automatically resends the emails that failed from the previous day.

The scheduler processes up to 100 emails at a time and reattempts to send.

This ensures that any temporary issues do not cause emails to be permanently missed.

Some additional information on M365 Mailboxes:

1. Email Send History

We store a history of successfully sent emails, giving us clear evidence of what has been delivered

To manage storage efficiently, older history entries (around 1–2 months old) will be periodically deleted.

2. Enhanced Error Logging

Our error logging capabilities include:

The system records internal errors, token‑related errors, and any API‑level issues in a dedicated error log table.

This allows us to reprocess failed emails either manually or automatically via the scheduler

If an email has failed to send through the M365 mailbox, this will therefore re-attempt to send on a nightly schedule. If you are experiencing high volumes of these or need further information on why particular emails failed to send, please contact isupport@abavus.co.uk .