Mail Delay when receiving mail from Microsoft Cloud (Office 365)

Hallo Gernot,

Kiekema hier: https://docs.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges?view=o365-worldwide

I'lI bet you can use just a few of the IPv4 subnets from there for a greylisting exception.  You can see what IPs were greylisted and then passed in November with:

     zgrep 'Successful greylist retry' /var/log/smtp/2021/11/*|grep -oP ' from .*? \('|sort -n|uniq -c|more

Please let us know which subnets you used.

Cheers - Bob

Hi Gernot,

graylisting isn't a feature to block a domain/sender ...

Every connection attempt user -> user may be graylisted at the first attempt.

The next attempt passes because there is already a graylist entry.

Afterwards, the next communication may pass too ... except something changes ... sender IP-for example. I think this is what we see with O356 often.

Greetings from Potsdam,

Greylisting is a feature from the past. The actual value of this feature was even then not the highest. Nowadays, the usage of greylisting was drastically reduced in the last decades due the disadvantageous and as better techniques came up. 

https://en.wikipedia.org/wiki/Greylisting_(email)

Well, Toni, I appreciate that it likely doesn't stop many spams that wouldn't be stopped by the SMTP Proxy's other antispam tools, but I just took a look at a small install and found that more than 2 out of 3 greylisted emails were not resent.

# zgrep 'Successful greylist retry' /var/log/smtp/2021/11/*|wc -l
432
# zgrep 'Greylisted' /var/log/smtp/2021/11/*|wc -l
1357

Cheers - Bob

This could be a success story or it could be: 2 of 3 emails are lost and could be legit. You never know. Thats the issue with Greylisting. Using a 4xx code to "please retry" could potentially loose you valuable emails.