452 4.1.1 <firstname.lastname@example.org> requested action aborted: try again later; info=mbY1luof9A3xl;mx4.tb;202105281425;220.127.116.11;
Thanks for this.
I am not a deep diving email expert but I have an idea that this 452 4.1.1 error may be generated as a result of some anti spam measures by VM. Alternatively. it could simply be down to a temporary server issue.
Often these errors include some explanatory text such as "Too many recipients" or "Too many emails sent in the last hour". However, in this case there is just the rather unhelpful "try again later".
The fact that the block seems to come into play when Sendgrid sends a large number of emails in a short period or when the emails are all very similar does support my anti spam theory, In the later case, the fact that the emails are very similar may cause VM to suspect that multiple copies of the email are being sent, again very spammer like activity.
The fact that Sendgrid's emails are only being blocked intermittently does seem to rule out:
1) Sendgrid's domain or iP address being blacklisted, or
2) that something with Sendgrid's outgoing email server setup is at fault.
Those are very common reasons for incoming emails being blocked but in both cases you would expect it to result in all Sendgrid's emails being blocked.
A copy of Sendgrid's outgoing email log for that email might offer more clues as to what is going on.
One of the real in depth email experts on this forum may well be able to provide more insight than I can. Alternatively, it may well need to be referred to VM's email security team. That will need to done by one of the Forum Team (VM employees who support this forum) and they should be along to pick up this thread in the next few days.
Either way, keep an eye on this thread for more insight into what is going on. In the meantime, as I said earlier, a copy of Sendgrid's outgoing email log for this email would be useful.
Sorry I cannot be more definitive. 😕
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