SMTP gateway issue

[#1]

No prob. I'm on my 3rd coffee!

I think disconnecting is just a short time out before I get chance to do the  EHLO.

Here's the response via TELNET

220 avasout-ptp-004 smtp relay.plus.net
EHLO relay.plus.net
250-avasout-ptp-004 hello [213.205.197.1], pleased to meet you
250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 104857600
250-PIPELINING
250-8BITMIME
250-STARTTLS
250 OK
AUTH login
334 VXNlcm5hbWU6
[Base64 username]
334 UGFzc3dvcmQ6
[Base64 password]
535 ...authentication rejected

[#2]

@red3 is there nothing after the '535 authentication rejected' ?

As @Townman suggested earlier, there's normally further details in the 535 rejection message

[#3]

Nope just: Connection to host lost."

C:\Users\Dell>telnet relay.plus.net 587
220 avasout-ptp-004 smtp relay.plus.net
EHLO relay.plus.net
250-avasout-ptp-004 hello [213.205.197.1], pleased to meet you
250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 104857600
250-PIPELINING
250-8BITMIME
250-STARTTLS
250 OK
AUTH login
334 VXNlcm5hbWU6
[username Base64 encoded using Notepad++]
334 UGFzc3dvcmQ6
[password Base64 encoded using Notepad++]
535 ...authentication rejected

Connection to host lost.

C:\Users\Dell>

[#4]

Ok, looking back through the thread, you say it was working yesterday.

Has your internet disconnected since then ? I'm thinking that you may have been allocated a different public IP which ghas a bad reputation. Even so, the telnet test ought be reporting the details, I dont understand why it isnt .

[#5]

I am remote so connecting over a tethered iphone on Plusnet mobile not from my home Plusnet broadband.

It has been reliable as a means of comms for many years and like I say working only yesterday.

[#6]

I am remote so connecting over a tethered iphone on Plusnet mobile

Ah! has that always been the case since it started failing ?

If so it is almost certainly IP reputation. Mobile networks use CGNAT (Carrier grade NAT) , whereby the 'real' public IP is shared by many users. When someone else using the same mobile network has behaved badly e.g sending spam , then the public ip may have acquired a bad reputation and that will affect all users.

The good news is that the situation is usually transient and will disappear after say 24 hours. Sometimes turning mobile data off & on will establish a new connection and a different IP.

[#7]

Note SMTP on port 587 should be STARTTLS not auto.

Odd that the authentication rejection is not reporting the subtext.