Problems with emails returned due to blacklisting of server.

Avast Free Antivirus / Premium Security
1

I had a problem when all of a sudden a week or so ago many of my emails were being returned. The messages on them were saying things like your server 31.170.120.34 was on a black list. I contacted my isp Vidahost (cloud hosting) who were very helpful but eventually came back with the fact they thought it was my virus scanner causing the problem. Sure enough when I switched off outgoing mail scanning in Avast everything was fine. Switch it back on again and get returned emails. Can anybody explain what is happening.
I am using windows 10, thunderbird and Avast. Defender is switched off. My wifes computer and my laptop have similar configurations and started the fault at the same time about a week or so ago. I have never had to switch off outgoing mail scanning before.
Obviously I have a cure. Switch off avast outgoing email scanning but I would love to know more. Anybody got a clue as to what changed and started the problem. Something in Avast or could it be Thunderbird.

2

There are some blacklistings on that AS :
http://urlquery.net/report.php?id=1482243889051

Possible explanation is that the IP is blacklisted because of sending (a lot of) spam, but only people from avast can tell.
I suggest to contact them > https://support.avast.com

3

Thanks. I realised that webserver is on some blacklists. However I think??? what Vidahost seemed to be saying was that it was Avast which was causing the email to go through that server. Certainly as soon as I switched off Avast outgoing mail scanner all was well. No more undelivered or returned email.

4

avast doesn’t select the mail server that is used, that is up to your mail client.

5

Thanks Eddy. Thats what i thought. However I still do not really understand what is happening. Vidahost have said
From the information you provided, I believe your issue is exactly as my colleague stated that HELO is changed to 127.0.0.1, because of your Avast. If there’s no specific configuration, regarding this, you’ll have to disable the Avast email protection.
I have done so and it all works fine.

When I have emails with avast outgoing email protection on they seem to come from these black listed servers, when this part of avast is switched off they seem to come from a different server. I was using the header information in the emails to glean this information.