Problems sending email to office 365 email accounts

[rafael.martinez]

Hello,

I have the following problem, I have a VPS and I am having problems sending emails to Microsoft Office 365 users, whenever I send email it shows me the following message:

Example 1:
SMTP error from remote mail server after end of data: 451 4.7.500 Server busy. Please try again later from [144.xx.xx.xx]. (S77719) [BN8NAM11FT057.eop-nam11.prod.protection.outlook.com 2023-04-18T18:11:48.633Z 08DB403641E6163C]

Example 2:
SMTP error from remote mail server after end of data: 451 4.7.500 Server busy. Please try again later from [144.xx.xx.xx]. (S77719) [BN8NAM04FT047.eop-NAM04.prod.protection.outlook.com 2023-04-18T18:12:03.730Z 08DB3F85D5C9782D]

Example 3:
SMTP error from remote mail server after end of data: 451 4.7.500 Server busy. Please try again later from [144.9xx.xx.xx]. (S77719) [BN1NAM02FT041.eop-nam02.prod.protection.outlook.com 2023-04-18T18:11:34.315Z 08DB403103A691EF]

I have received a form from Microsoft to see if the IP is on a microsft blacklist but they have replied that the IP is not on any of their blacklists.

 

[cPRex]

Hey there! Is the 144.x.x.x part of the Microsoft network? It would be best to contact their support with the output from your logs that you provided here to see if they could determine the cause of the issue. Since your server is sending the message and reaching the Microsoft network properly, there isn't anything else you can do on your side.

 

[rafael.martinez]

Hello,

The IP 144.x.x.x corresponds to the IP of my VPS provided by contabo.com

 

[cPRex]

Thanks for that - I just wanted to clarify what that was. You'll still want to contact Microsoft directly to see why that is happening for messages from your server. To me, it sounds like you are being ratelimited.

 

[rafael.martinez]

Hello,

Indeed, it seems that Microsoft limits the amount of email it receives from our VPS, I changed the VPS IP and the emails began to be sent, but after a couple of hours the problem returned.

We use VPS to send emails to our clients who mostly use emails provided by Microsoft, all emails are legitimate.

What can we do?

 

[mtindor]

Hello,

Indeed, it seems that Microsoft limits the amount of email it receives from our VPS, I changed the VPS IP and the emails began to be sent, but after a couple of hours the problem returned.

We use VPS to send emails to our clients who mostly use emails provided by Microsoft, all emails are legitimate.

What can we do?

Are you sending emails from domains on your VPS that have proper DKIM signing and SPF records active? Does the reverse DNS (rDNS) of your VPS IP address reflect a sensible name?

M