Cannot send email via SMTP (relay.plus.net) — "incorrect username/password" error despite correct cr

[#1]

Spoiler

Posting on behalf of my father, who holds a plus.com account, as I'm helping him troubleshoot an email issue.

He’s just been migrated to EE, but can’t recall if this email issue coincided with that change or predated it.

He's having trouble sending email via SMTP. Here's what's already been checked and ruled out:

- Webmail (webmail.plus.net): He can log in normally — confirms the password is correct.
- IMAP (incoming mail): Works fine on all devices — email is received without issue.
- SMTP (outgoing mail): Fails consistently with an "incorrect username/password" error.

This has been tested across multiple setups, all with the same result:
- On wifi (home broadband)
- On mobile data (4G) — ruling out any IP/network-level blocking
- After fully deleting and re-adding the account from scratch on iPhone (not just editing settings)

Settings used:
- Server: relay.plus.net
- Port: 587
- Encryption: STARTTLS (SSL off)
- Authentication: Password
- Username: full email address (dad's plus.com email)

Since IMAP and webmail both authenticate successfully with the same credentials, but SMTP consistently fails regardless of device or network, this looks like it could be an SMTP AUTH configuration issue on the account itself — possibly related to a recent account/mailbox migration.

Is there a way to check whether SMTP authentication is correctly enabled on this account?

Or any other suggestions?

Account email: [Removed]
Account holder's name: Brian Baxter

Thanks for your help,
Phil, on behalf of my father

Moderator's note by Mike (Mav): Personal information removed from a public forum (to an area that staff can see).

[#2]

Appears setting smtp server to mail.enmail.co solves this

brilliant job plus.net is communicating this to a 87 year old

[#3]

Reads like Plusnet have now closed the a/c at which point access to SMTP relay.plus.net is lost.

Greenby SMTP servers to try are : relay.force9.net or mail.enmail.co      ( as a direct replacement for relay.plus.net )  

Both support SMTPS ( Port 465 ) and STARTTLS ( Port 587 ) encryption options and have a valid Certificate.

Note the Username needs to be the email address i.e. NOT <account>+<name> and NOT an alias.

[#4 · Accepted solution]

"Posting on behalf of my father, who holds a plus.com account, as I'm helping him troubleshoot an email issue.

He’s just been migrated to EE"

So he no longer has a Plusnet account!

"...but can’t recall if this email issue coincided with that change or predated it."

"He's having trouble sending email via SMTP."

It is because he no longer has a Plusnet account, so cannot log in to the Plusnet SMTP mail host.

You don't mention if he has been transferred to Greenby - I assume he has been. He/you can check all is OK by logging in at the Greenby portal (greenby.com) using his Plusnet account username and Plusnet account password.

Assuming a Greenby email account and no longer a Plusnet account holder, I believe the outgoing SMTP host will need to be changed to mail.enmail.co, port 465 with Encryption turned on.

[#5]

@PhilipHeyes  / @pvmb - the OP sorted it -see post #2. 😃

[#6]

@pvmb that the Webmail and IMAP continue to work, suggest the a/c may well have migrated to Greenby.

We are about to find out.

Scrub that,  it is fixed.