550 5.7.501 Service unavailable. Banned Sender. - no help from Support

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I've sent out less than 400 emails using SMTP today (while keeping in mind https://technet.microsoft.com/en-us/library/exchange-online-limits.aspx#Receiving%20and%20sending%20..., so 30 mails every 62 seconds). Yes it's a once in a year peak but never the less within the limits of O365.


So I've been banned. Now I can't send the reaming 37 emails I should urgently send out and additionally while https://support.office.com/en-us/article/email-non-delivery-reports-in-office-365-51daa6b9-2e35-49c4... states "To restore this account’s ability to send mail, please contact support through your regular channel" support did not help at all but suggested to wait 24 hrs.

This is rather disappointing for a professional service! Please help!

Thank you

P.S. There are no account issues to resolve! I sent the emails I wanted to send!

5 Replies

30 messages over 62 seconds is very close, it would only take a small disagreement on the timing between Microsoft's calculation and the tool you are using.




Good point: But the program needs another 20-30 s to send the emails so it's actually much more (at least 80s per 30 mails)

Update: I've added a log which clearly shows I never as near the 30 mails per 60s limit:

Update2: Didn't work, so I put it on PasteBin: https://pastebin.com/EVRH4q1g


But is that additional equally spread between each message, Microsoft will only see the SMTP connections, maybe your app takes 30seconds to get ready before it starts sending the first SMTP.


Absolutely my personal opinion, but I would always aim for 50% or any threshold value and double any time estimate.


Thank you for your help:
Please let's split up this discussion in two things

a) Currently my real issues are that:
1. I can't send mails using MAPI / Outlook / OWA
2. Internal messages that are automatically forwarded (by a forward setup by the user) are not forwarded if they are from me (because I'm banned).
3. I as an Admin can't resolve this.

b) Regarding the mass mailing:
1. I'd like to mention that this worked just fine the last years.
2. I clearly never sent more than 30 mails per 60 seconds (or within a specific minute)
Actually per SMTP connection 30 mails are sent. Then the connection is closed and the app sleeps for 62 seconds. Then a new SMTP connection is established.
Never the less I can change the settings as you suggested but I wonder why those limit are posted if the recommendation in the end is to do half of it?

Thank you


Update: Also why would I be banned and not temporarily blocked when going over the 30 mails per minute? It seems to be a rather harsh approach!


So in the end it was really simple:

Exchange Admin Center > protection > action center and unblock the user (me).

Why is this not mentioned here? https://support.office.com/en-us/article/email-non-delivery-reports-in-office-365-51daa6b9-2e35-49c4...

Additionally I wonder how long I would have waited for the solution if didn't open a second ticket and got lucky...