Advice needed: Security Warning using Outlook Microsoft 365

[#1]

On a recently bought second laptop  I am now attempting to setup an email account using Outlook 365 This is a duplicate of an account which was setup and has been in use for some years now on my first computer also using Outlook 365. The laptops are not networked

1. On the first laptop the settings for this email account are

Incoming Mail server imap.plus.net        Port 143

Encryption Method                                   None

Outgoing mail server imap.plus.net         Port 587

Encryption Method                                   None

1. Using These settings on the second laptop, the connection is timed out

But what does work is (which appears to be Outlook’s default setting) :

Incoming Mail server imap.plus.net          Port 143

Encryption Method                                   None

Outgoing mail server smtp.plus.net          Port 587

Encryption Method                                   STARTTLS

• My outgoing (STMP) server requires authentication
• Use same settings as my incoming mail server

But in doing so I get the security warning that the certificate cannot be verified.

So please what settings should I be using ?

[#2 · Accepted solution]

Looking at the certificate that 'smtp.plus.net' serves up, it doesn't actually cover the 'smtp.plus.net' name itself hence Outlook is likely rightly rejecting (or at least complaining about from what you've said?) the connection on the grounds that it could be masquerading as 'smtp.plus.net'.

Try changing it to relay.plus.net instead as that resolves to the same machine(s) and is the subject name on the certificate so should verify.

Incidentally, I am surprised your previous settings worked as there's no SMTP/Submission service listening on 'imap.plus.net'. 🙂

[#3]

Good spot about the outgoing server name, @MJN - 'smtp.plus.net' is definitely wrong - as the OP should see from the details supplied in the PN mail set-up instructions.

[#4]

Yes thank you for confirming the need to change to  relay. plus.net. for outgoing. It works. 

[#5]

Yes I did note the set-up instructions. As it is, the account in question is  a waitrose.com email address which I have had for 15 to 20 years.  This is a legacy account  set-up some years before the waitrose broadband service was incorporated into the John Lewis Broadband service. I did not have to set-up the account using  "Manage My Mail" . This may perhaps explain why the  imap. plus.net works for outgoing mail on the first laptop?.

[#6]

No not at all - how the mailbox is set up has nothing to do with the mail collection server addresses.  It is odd that imap.plus.net works for out bound at all.