Trying to setup external SMTP relay with Microsoft 365 to allow high send rate.
Looking at services like SendGrid, MailGun etc. but struggling with the fact they all use basic auth and Microsoft is actively blocking this.
Ideally want to set this up so a handful of users can be given access to the Comms / Marketing email and do a mail shot to 15k+ recipients.
Avoiding them using the SMTP service’s UI so they don’t need to upload and maintain 15k+ contacts. Unless someone knows of an automated integration the can sync the global directory.
Outlook client doesn’t allow manually editing SMTP when you’re using cloud exchange. Mail on a Mac was the same.
IMAP doesn’t work as Microsoft don’t really support it well. Even if we put in bypasses and policies to try and make it work we’re getting auth failure during validation so can’t set the account up.
Same issues with PC and Mac clients, otherwise could set up manual SMTP.
Tried building a Mail Connector but that too fails to authenticate as it doesn’t validate the SMTP service because they don’t allow you to enter credentials even for outbound connections. So the service just responds with a 550 error. Ignoring the failed validation, can push messages out but the SMTP servers reject any attempt as unauthorised.
Ideally need an SMTP relay that supports modern authentication.
Failing that a way to sync the Exchange address list into the Contacts section in the SMTP system would make life way easier. Low code options require the contacts to by in the mailboxes My Contacts for sync. It won’t look at the directory.
Looked at low code integrators that could possibly take an inbound email and forward it on to SendGrid but that would only work with a fixed recipient list and we want to use dynamic subgroups so triggering from an inbox event isn’t ideal.
Otherwise it’ll have to be an app that we create which will get very messy and require a UI and it quickly becomes complex.
You’d think this would be a common problem that’s solved for big enterprises already.
Currently got a hack in place using HubSpot marketing tools but needs manual upkeep of the contacts which is a nightmare.
Any ideas welcome.
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