Major issue sending emails from MS Office Outlook through PlusNet to gmail addresses

[#1]

I use PlusNet as my broadband provider for which I have a PlusNet email address

I also have a Gmail account with a Gmail email address

I use the MS Office Outlook built into the MS Office 2010 Pro software suite on my PC for sending and receiving emails and have done so for many years without issue.

In the last couple of weeks, I have realised that any emails that I have sent to anyone else who has a Gmail email address has not received my emails.

I have not received any error messages from anywhere and neither have these emails gone into any spam box along the way. Even if I email myself from Outlook, the email gets lost altogether.

Emails sent to my Gmail address are forwarded from Gmail to my PlusNet a/c and this is linked to the Outlook on my PC which downloads those emails to my PC.

Likewise, any emails sent to my PlusNet email address download on to my PC by that same link.

Emails sent from Outlook on my PC are sent out with my Gmail email address (as the sender) but go through the PlusNet servers to send off to the intended recipients.  However, it is this which appears to have become corrupted in some way.

I don’t believe that I have changed anything and am really struggling to get any resolution to my problem.

Hence my asking for some HELP please .......................

[#2]

should have included this diagram

[#3]

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@BasherB wrote:

Emails sent from Outlook on my PC are sent out with my Gmail email address (as the sender) but go through the PlusNet servers to send off to the intended recipients.  However, it is this which appears to have become corrupted in some way.

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Forwarding emails into one mailbox then attempting to send as the forwarded from-email-address is asking for massive trouble.  Why bother with forwarding Gmail emails?  It just creates confusion.  Configure the Gmail account separately within Outlook.

Emails sent from you@gmail.com should go through Gmail's SMTP servers, not Plusnet's.

Nothing has been corrupted, but Gmail are enforcing use of SPF protocols which determine which SMTP services are legitimate senders of @gmail.com emails.  That does NOT include Plusnet's relay servers.

If you have (apparently) similar issues sending from your own domain name hosted on Plusnet's mail services, that is a different issue, even though the symptoms might look the same.