Plusnet Greenby emails greylisted then fail

[#1]

We are having difficulty in sending emails to contacts within a local council. The error message which covers back is that the Plusnet domain is greylisted. It seems that the receiving mail server is set to wait for a retry from the Plusnet server from the same IP, but that it detected that the IP changes every time, so after about 8 retries, it fails and a failure message is sent by the receiving server.

Would this be normal that the emails would appear to come from a different IP for reach retry?

[#2]

@Stuart22 

Would this be normal that the emails would appear to come from a different IP for reach retry?

Its quite likely, there are a number of outgoing mail servers (typically avasout-peh-<nnn>). Whilst their IPs may be slightly different they are all in the same /24 subnet.

Sounds like the council's greylisting is flawed or badly configured. Normally a resend from a IP in the same Class C (/24) subnet would be accepted.

edit: has your email account been migrated to Greenby ?

are you still sending via relay.plus.net ?  

[#3]

Yes we have migrated. One thing that had just occurred to me is that the messages are failing when sending through an Imap account on Outlook Classic, while it does seem to be sending OK from a phone which uses the POP3. Relay.plus.net account. I'll try setting Outlook as POP3.

[#4 · Accepted solution]

POP3 & IMAP are incoming connections, they have nothing to do with outgoing mail, that is SMTP.

One thing that had just occurred to me is that the messages are failing when sending through an Imap account on Outlook Classic

I suspect that Outlook may be using the Greenby server (mail.enmail.co), its pretty good at changing settings to what it 'thinks' is the correct setting.

I dont know how the Greenby servers are organised, my earlier details refer to relay.plus.net.

If Outlook is using mail.enmail.co, then you may have to ask Greenby how their servers are organised.

[#5]

Greenby SMTP mail.enmail.co also has multiple out bound servers each with a unique IP.

[#6]

Are they all contained in the same /24 subnet ?

[#7]

The most recent ones were :

anabella-rose.gateway.enmail.co   213.5.183.26

arabellina.gateway.enmail.co   213.5.178.136

joelle.gateway.enmail.co   213.5.181.208

[#8]

It would need a /21 subnet to cover those. I wouldn't be surprised if greylisting fails in that case.

[#9]

Oh of course, sending is through SMTP either way.

I've just sent an email to myself from both the phone (which is using IOS mail and does reach the recipient) and Outlook on laptop (which is greylisted). The headers look similar in that they come from mail.enmail.co but the IPs are different. Also, with the email from the phone, after the DKIM section, the second Received section mentions received from smptclient.apple, and another DKIM section, whereas the headers from Outlook, after the only DKIM section, it is just another received from mail.enmail.co.

I'll test with another email client such as Thunderbird, otherwise might need to switch to gmail to send to this recipient.

[#10]

OK on checking the Outlook settings, the automatic account configuration had indeed chosen mail.enmail.co as the outgoing server. Once I changed that to relay.plus.net, port 587, STARTTLS and normal password authentication, the emails started getting through. (even though going through relay.plus.net still results in the email headers including mail.enmail.co - that's what was confusing)

Thanks all for the help

Stuart