@sandrined and @ptdradmin both reports not to receive mail from the MediaWiki Saas:

• Microsoft/Outlook/Hotmail: silent reject (as confirmed by other sources for now several years for new mail domains)
• Gmail: explicit message SPF is required

Note: Works for Google Workspaces mail (tested to @espace-win.org for example).

Plan:

• use subdomain wikis.nasqueron.org for mail
  • A is already OK
  • SPF to add to whitelist the web-001 IPs
• update configuration to use this new mail domain

At this stage, it should work for gmail, and we'll be able to test with Microsoft servers too.