Only 20% of contacts were successfully sent to, others had 'unknown issue'. No trace in exchange mail analysis for any of them
There are some issues still to resolve. Only 198 of my validated 1394 contacts were successfully sent to, other with 'unknown errors' and no means to try a resend to them (Consider RESEND function to those who hadn't received it?).
Using Message tracing gave no clues as no failed or successful trace information exists there (Consider adding send info to message tracing in the admin centre?).
Glad you noticed the fix! We automatically retry sending the campaign to contacts if the issue was temporary / transient so there should be no need for any actions on your side. As you might have noticed it would have sent the email to any valid recipients that we initially dropped for various reasons.
I believe this may have been fixed. My contacts seemed to update themselves, then the sending process restarted and all contacts were successfully sent to. Many thanks.
Further to above, it appears there is a delay in adding contacts correctly to mailing lists and the mailing list itself doesn't get populated fully until quite some time after, despite increasing the number shown in contacts (but only after a delay to the mailing list). I'm guessing the above issue was because I was attempting to send to contacts which had not fully integrated to the mailing list (the mailing list number in the graph only reached 198 before I sent the mail out, despite me adding 1394 contacts to it sometime prior), causing the unknown error. Still requires a fix.