Unable to send email through Apple Mail program

[racranston]

I am using a MacBook Air  (Tahoe 26.2).  Since the 17/01/2026 I have been unable to send an email from the laptop using Apple Mail.  Until today I wasn't able to send email from my iPhone. either!  ( - ios26)  but after much too-ing & fro-ing the phone  seems to be working at the moment

When attempting to send an email I get message

"The sender address.........(my email)...............was rejected by the server mail.btinternet.com.

The server response was: authentication required - Your email could not be sent. To fix this you must make a simple change to your email client (known as SMTP authentication). For advice visit http://www.bt.com/smtp

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent.  "

I have tried various tweaks of the outgoing mail settings , my settings seem to be as indicated at http://www.bt.com/smtp 

 I go to settings for outgoing mail server- there is only one on list "Btinternet "- which has SSL on, server port showing 465  and have keyed in a password for authentication- using the  password for my btmail account. but still no success.  

any suggestions gratefully 

[gg30340]

Are you presently a BT Broadband customer or are you paying for your email through a BT Premium email account or did you migrate to EE Broadband?

The correct settings for BTMail are in this link.

BT Email server settings | BT Help

[racranston]

Thank you for response.  I am not a BT broadband customer - I only have BT premium email account.  my outgoing email settings seem to be as indicated under the SMTP settIngs on BT website help page link you provided.  My only doubt is the  "authentication: PLAIN"  . I don't seem to have this option

[licquorice]

Perhaps asking on an Apple forum might reveal how to make the correct settings.

Mail apps usually have the option to either send the password in plain text or encrypt it, as the whole connection is encrypted (SSL) the password needs to be sent in plain text rather than doubly encrypted.

[racranston]

thanks again.  although I am not entirely sure what you mean by plain text.  I'll have a look around the apple site for help.  I spoke on the phone to bt helpline but they couldn't offer any solution aside from speaking to apple.

this  is not how I envisaged spending much of my day off from work!

[licquorice]

As explained, plain rather than encrypted