Email not being received (timeout)

[Rob_D]

We're not receiving emails from a specific domain. Two different email accounts from the same external domain show the below error and then fail delivery. The error appears to happen after Our mailflow rules have applied.

The error's we're seeing are:

Reason: [{LED=450 4.4.315 Connection timed out [Message=Socket error code 10060] [LastAttemptedServerName=31.221.81.58] [LastAttemptedIP=31.221.81.58:25] [SmtpSecurity=-2;-2] [AM7PEPF0000004F.eurprd07.prod.outlook.com 2026-04-22T13:43:42.570Z 08DEA0458C12BEF3]};{MSG=Socket error code 10060};{FQDN=31.221.81.58};{IP=31.221.81.58. OutboundProxyTargetIP: 31.221.81.58.

 

Everything I can find points to a misconfigured server link or firewall, but we're Office 365 with no on-site exchange server and emails from other domains don't have the problem.

[pete]

Have you ever received email from them successfully?

Can you email them OK?

Is something actually listening on port 25 of that IP (31.221.81.58)?

 

[Rob_D]

Have you ever received email from them successfully?

Not to my knowledge.

Can you email them OK?

Apparently no. Although no errors our side going that way.

Is something actually listening on port 25 of that IP (31.221.81.58)?

No idea, not my IP range.

[pete]

Are they more than 500 miles from you? 😀

 

https://www.ibiblio.org/harris/500milemail.html

[tom_newton]

What's your email domain? Does that look like something in your MX?

(My guess is some sort of janky DNS issue their end)

[ChrisC]

Are you (or they) using any upstream email protection like Barracuda etc? 

 

Is their email exchange online/Gmail or something on-prem/more custom?

 

It sounds like a connector/gateway misconfiguration on one of the ends.

 

To continue Tom's thinking, have you had a look at their MX record as well to see if there's anything obviously funky? 

 

If you're both running exchange online, you wouldn't expect to see raw IPv4 as the server endpoint unless there's some custom routing going on.

[PaddyNewman]

That IP has refused connections on port 25 from all my test endpoints, doesnt make it impossible, but ive tried to say hi from multiple sources and they've timed out each time. 

 

That range is expo-e so customer of theirs i guess. That mail server looks less mail servery right now. 

[Rob_D]

We're not using any upstream protection, I don't know about them. As far as I can tell, they're M365 email and the MX records look good.

[ChrisC]

It looks like Paddy's tried to talk to the IP listed above (assuming this is your side as you mention the receive errors).

 

Any legacy connectors (potentially that IP) in your exchange online setup that might be getting selected?

[Rob_D]

I've looked in the obvious places in the Exchange Admin center (as in, I looked under the Hybrid exchange settings) and couldn't find anything. But thinking about it, we did have Exponential-E internet and were running hybrid exchange about 10-15 years ago, so maybe. Time to go through the whole admin console looking for something I missed.

 

Although I don't get why this one particular domain would be a problem.

[ChrisC]

Have you checked in exchange admin center > mail flow > connectors?

 

It could be that the exponential IP is listed in one of the connectors.

[Rob_D]

Ahh found it, for some reason the inbound connector had been left on. 🙄