problems with email to gmail addresses bouncing back

[#1]

Everytime I email someone with a gmail address I get this message (I've deleted the recipient's email address):

"This is an automatically generated Delivery Status Notification.      

Delivery to the following recipients failed permanently:

(name of person's gmail address)

Reason: A message that you sent to the following recipient could not be delivered due to a permanent error. ** The remote server ?? responded with: ** (name of gmail address)??:?? This message was created automatically by mail delivery software on the server .

Reporting-MTA: dns; avasout-peh-002 [212.159.14.18]

Received-From-MTA: dns; [192.168.1.64] [87.115.153.9]

Arrival-Date: Tue, 27 Jun 2023 08:53:32 +0100

Final-recipient: rfc822; (gmail address)

Diagnostic-Code: smtp; 550-5.7.26 This mail is unauthenticated, which poses a security risk to the"

Any ideas? Have checked all of the settings my end. Also its happening irrespective of what device I use. Thanks in advance.

[#2]

Moderators Note

This topic has been moved from Broadband to Email

[#3]

@outinthesticks have a read through this thread https://community.plus.net/t5/Email/Replies-to-Gmail-accounts-being-rejected/m-p/1914789#M42617 and then post back with questions

[#4]

Thanks, read through the thread you posted but got lost after the second screen. I'm not sure where I find where connection security and SMTP settings are - I attach a screenshot of the settings on my IMac. 

[#5]

Its nothing to do with security settings on your email client, its the lack of SPF or DKIM on the domain you use for your email.

[#6]

Thanks. I've tried to add an SPF record so will wait and see if that has worked. In an earlier thread someone said "also you should change your SMTP connection security to STARTTLS and use port 587" hence my query, but I'll wait now and see if the SPF record does the trick. Thanks for your help.

[#7]

Can we clarify the context here please - what email address / account are you SENDING from...

• A Plusnet email account or a legacy brand (MAAF) email account
• you@youraccount.plus.com
• you@yourdomain.co.uk which is hosted by Plusnet (or MAAF)
• you@yourdomain.co.uk which is hosted elsewhere which forwards  mail to your Plusnet (or MAAF) mailbox

As for those server settings shown in the screen shot...

1. SMTP should use Port 587
2. iMAC does not show STARTTLS but will work it out if you tick "Use SSL"
3. Under Options... I expect that there will be authentication setting details - these need to be the same as those for the  inbox

In passing POP3 inbound ought to be encrypted, on Port 995 with SSL