Trouble sending to gmail recipients – Tools

Over the past few weeks, I’ve seen the following occasionally when I try to send an email to someone who uses gmail, I get a “Undelivered Mail Returned to Sender” with the following in the message:

host[xxxxxxxx] said: 550-5.7.1 [xxxxxxxxx] Our system has detected that 550-5.7.1 this message is likely suspicious due to the very low reputation of 550-5.7.1 the sending IP address. To best protect our users from spam, the 550-5.7.1 message has been blocked. Please visit 550 5.7.1 Why has Gmail blocked my messages? – Gmail Help for more information. xxxxxxxxxx (in reply to end of DATA command)

If I resend the email, it typically goes right through.

Sending email to my own personal Gmail account and select “show original” from the menu, I see:

So it seems my mail server is set up fairly well. Perhaps my SMTP credentials have leaked, but my server is not showing up on any of the DNS blacklists.

The hazards of running your own email server – the fundamental problem may be that the big email providers make it difficult to send email to them

Google has Postmaster tools – I signed up for this, and looks like they can collect data for you – will check back in a couple of days:

For the past two days, late in the day, email to google/gmail recipients are getting blocked. Earlier today, it was working fine. Even sending to my own gmail address is now blocked. Guess I’ll try again tomorrow.

Same pattern holds – last evening, I could not send email to any gmail recipients, even my own gmail account. This morning, it is working fine. This seems a little more complicated than a simple blacklisting – perhaps some automatic algorithms have run amok. still does not show any data from my domain. Looking at this thread, it seems there needs to be a certain volume of mail required:

The Gmail PMT does require a certain volume to analyse and display the details. Hence I prefaced with “if you happen to send out a fairly large number of emails to Gmail users…”. Hopefully, with time, that volume will be reached and the details displayed.

As for the message, it is impossible for me or anyone else to accurately discern the suspicious component because that it determined by references to Gmail’s own algorithm and information from reputed blacklists, crowd-sourcing and user preference not to mention the details included in the guidelines help article, plus the content of not just the message, but also anything included in the signature.

It seems if my server was being used to send spam, than there would be plenty of email volume sent to gmail users.

digging through the SMTP server logs – there are only 3 users, a wordpress site, and a git server that use this mail server. In the last month, there were only 244 messages sent. Most of the messages were business related messages sent from me. It does not appear that the SMTP credentials have leaked or anything like that.

I asked about this on reddit. One person responded:

This is why EVERYONE tells you not to selfhost email.

However, email is about the only widespread decentralized communication platform, so it seems healthy to keep it this way, instead of everyone routing their mail through two large companies. So I’m a bit stubborn in this regard, and perhaps a bit of an idealist …

This issue is also a potential problem for google mail users – if people can’t contact you (especially potential customers, etc), is that a problem? In our effort to stamp out every little last bit of spam, there will also be collateral damage.

yesterday gmail SMTP was not working for me either in Tbird but today its ok.

I just learned every time my mail gets blocked, the transaction is using IPv6 addresses. So not sure why it uses IPv4 sometimes and IPv6 at other times. This is very likely the issue …

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