SMTP error from remote mail server after end of data: 554 mail server permanently rejected message (#5.3.0)

[Bin Emmanuel]

This morning I got a message from the office saying they weren't able to send an email to a particular recipient the email contains an attachment a .pptx file which is ~15MB in size.
I did a lot of digging to figure out what the problem might be and from what I learnt the issue might be a result of bad DNS from my end or the recipient server blocking ours. Now looking at my DNS records it seems everything is fine and I've not been able to convince anyone at the office that the problem isn't from us and I'll really appreciate a hint to solving the problem permanently.

 

[cPRex]

Hey there! It's clear from the bounce message that the problem is likely not on your end since it says "mail server permanently rejected message." Now, this could be because they determined your message was spam, or your IP address is on some type of block list on the recipient end, but with the information we have there is nothing you can do on your server to resolve this issue. Since the message does reach the recipient mail server, that rules out a DNS issue.

The only thing you can do is contact that remote mailserver using another email address to see if you can get more details on why they are rejecting your messages.

 

[Bin Emmanuel]

I just ran a quick blacklist check to find out that my server IP Address has been blacklisted by UCEPROTECT. Can this be what the recipient uses?

 

[cPRex]

It's possible, but no one generally takes that blacklist seriously. But yes, if they are using that list and you are on it, that could be one reason your mail isn't getting to them.

 

[Bin Emmanuel]

What could have been the reasons why the UCEPROTECT blacklisted the IP Address?

 

[cPRex]

As I mentioned earlier, they are a blacklist that no one should take seriously. I wouldn't worry about being on that list at all. Read this page to get an idea of how they operate: UCEPROTECT®-Network - Spam protection made in Switzerland

This also gives some more detail:

UCEPROTECT Email Protection Scam • Conetix

UCEPROTECT is a Realtime Blackhole List system, which like many other RBL's is used to reduce the amount of spam by ranking the IP address of the server

conetix.com.au

 

[Bin Emmanuel]

Now I'm wondering if changing my IP Address might solve the problem since I would be getting one that isn't blacklisted. The thing is I don't know why the IP Address was listed at UCEPROTECT and even though I understand it to be ransomware I still need to get my IP Address off its list because some recipients still use it and these recipients are really important to the company. If I knew why they blacklisted our IP Address I'd rather fix the problem and be whitelisted instead of switching to a new Server with a different IP Address.

 

[cPRex]

The best thing to do would be to contact your hosting provider or datacenter. However, if you're only seeing problems with email to this one particular location, it would be best to reach out to them through an alternative email address to see if they can provide you more specific details on why you are blocked.