Microsoft are retiring traditional SMTP access from March 1st, no exceptions!

Alternative could be to use a non Office365 SMTP relay.  These instructions are for Office365 only.

To use Office365 to send email you need to add the following:

1. You will need an Application Registration if one is not already setup for Sysero in Azure Driectory.
2. We would recommend configuring this so mails can only be sent from a single shared mailbox (shared to avoid unecessary user license).
3. This is done by creating a mail enabled security group in the Exchange Admin interface.  And adding only a single member of the mailbox you want to send from.
4. Open Azure Powershell
   Connect-ExchangeOnline
   New-ApplicationAccessPolicy 
       -AppId <Sysero-App-Id> 
       -PolicyScopeGroupId "thesecuritygroup@domain.com" 
       -AccessRight RestrictAccess 
       -Description "Restrict app access to this group".
5. Note above is security group email not the one you will be sending from.
6. You can test this before setting up next steps using Test-ApplicationAccessPolicy -Identity user@domain.com -AppId <Sysero-App-Id>.  Try with shared mailbox you configured it should have access to and any other e-mail it should not.
7. Application Registration needs Application Level Graph permission of Mail.Send.
8. web.config in Sysero must have "smtpmode" app setting set to "graph".
9. All other settings to app level registration are set as usual for other OAuth app level calls.
10. Email from and Email templates must have FROM address set to one that is specified in the security group (not the security group email but the shared mailbox).
11. Note you can setup other shared mailboxes and add them to the same group, if you want multiple from addresses.