Posting this as it might be useful for others.
Thank to @Protech for this initial advice hints.
I've been migrated to Greenby (since about New Year).
I'm receiving emails OK (using mail.plus.net Port 995) (although I had to increase my "whitelist scores" to make the filters "less aggressive" in order to get emails directly into my Inbox - rather than into Junk at Greenby! - But that's a separate issue!)
I too have being having major issues sending emails to Microsoft accounts. But I can now send to Microsoft accounts by using mail.enmail.co Port 465,and setting encryption to SSL/TLS (rather than STARTTLS). At least I haven't had any bounce-backs yet from Microsoft accounts.
But I also had to change my "logins". To login to my incoming server (mail.plus.net) I need to use my PlusNet username (NOT my PlusNet email address) and password. When using the PlusNet outgoing (SMTP) server, I could simply use the same login details. However, when using the Greenby (mail.enmail.co) outgoing (SMTP) server, I had to change my login details to be my email address and password (NOT my PlusNet username). I tried to use my email address as the login details for the incoming server (mail.plus.net) - so that the incoming (PlusNet) server and the outgoing (Greenby) server used the same login details, but that didn't work.
But......... (there's always a but!) using Greenby outgoing server - I now can't send emails to iCloud accounts 😞 See error messages below:
Reporting-MTA: dns; gateway1.enmail.co
X-Postfix-Queue-ID: 5F6234247F
X-Postfix-Sender: rfc822; xx@yy.plus.com
Arrival-Date: Tue, 3 Mar 2026 16:04:28 +0000 (UTC)
Final-Recipient: rfc822; zz@icloud.com
Original-Recipient: rfc822;zz@icloud.com
Action: failed
Status: 5.7.1
Remote-MTA: dns; mx02.mail.icloud.com
Diagnostic-Code: smtp; 554 5.7.1 [BS01] Message rejected due to local policy.
Please visit https://support.apple.com/en-us/HT204137. Txn ID
1c783302-6b57-49c6-a4b0-e4efd69e246f
This is the mail system at host gateway1.enmail.co.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
<zz@icloud.com>: host mx02.mail.icloud.com[17.56.9.31] said: 554 5.7.1
[BS01] Message rejected due to local policy. Please visit
https://support.apple.com/en-us/HT204137. Txn ID
1c783302-6b57-49c6-a4b0-e4efd69e246f (in reply to end of DATA command)
When using the PlusNet Server, I couldn't send to iCloud accounts if I sent to multiple addresses at the same time, but I could send to iCloud accounts if I only sent to one (iCloud) account at a time.
It appears that when using the Greenby Server, I can't send to iCloud accounts at all - not even to a single iCloud account at a time.
So (thanks to @Protech ) I've managed to solve one issue, but swapping to Greenby servers appears to have a created another. (**Sigh**)
My solution (which is a real faff), is to use Greenby Servers for sending outgoing emails to all my contacts, see which ones bounce (from iCloud). Then change my outgoing server back to PlusNet. Re-send the bounced emails (individually) to the iCloud accounts. Then change my outgoing server back to Greenby.
This is far from ideal, but at least I can email all my contacts - and is probably less grief than getting another email address and having to update everyone - although that will probably be the ultimate way forward.
I've raised a ticket with Greenby about not being able to reach iCloud accounts - but I'm not holding my breath for a reply - never mind a solution!
