Linux Mint only has problem with sending emails out

[#1]

Hi, I am having problems dealing with my emails in Linux Mint.  I have Thunderbird as my email client.  All other emails are fine, but the problem started when I changed the main accounts password a few weeks ago.  When I send an email from my email client and from my main email account I get this:

Quote

An error occurred while sending mail. The mail server responded:  <*******@*******.plus.com> sender rejected - invalid domain (no MX or A record).  Please verify that your email address is correct in your Mail preferences and try again.

The email and all the other details have been left the same, the only difference is, is the password change.  I deleted the old password from the saved passwords, but I cannot get it to resolve the problem of sending the emails.  Its quite frustrating as it should be a simple task, but obviously not to my stupid morphined brain.  Can any one assist please.  
I love using Linux as its a safer OS than WIndows.  I do have a dual boot, which gives me the best of both worlds
Thank you for reading just hope you can assist
Thanks

[#2]

Sounds like you have Thunderbird configured for authenticated smtp. You need to change the password on the outgoing server settings.

[#3]

Quote from: TonyPhotoplus

Quote An error occurred while sending mail. The mail server responded:  <*******@*******.plus.com> sender rejected - invalid domain (no MX or A record).  Please verify that your email address is correct in your Mail preferences and try again.

That's a fairly explicit error message and it doesn't imply it has anything to do with the password. Instead it suggests that either the sender or recipient address of the email you're trying to send cannot be resolved in DNS. e.g. try sending /from/ an invalid email address and you get this:

$ telnet relay.plus.net 25
Trying 212.159.9.107...
Connected to relay.plus.net.
Escape character is '^]'.
220 avasout03 smtp relay.plus.net
ehlo relay
250-avasout03 hello [84.93.219.165], pleased to meet you
250-HELP
250-AUTH LOGIN PLAIN
250-SIZE 104857600
250-PIPELINING
250-8BITMIME
250 OK
mail from:<this@isnotvalid.tld>
550 <this@isnotvalid.tld> sender rejected - invalid domain (no MX or A record)

[#4]

Thank you for your input -  I am totally confused.  Mind you that is easy with me living on 400mg morphine a day.  The old brain don't do so well as its pickled!  I did all happen when I changed the password to the main email account and to Plusnet.  The other accounts are working fine with the same settings.  Its too confusing to work out and resolve at the moment.  So can anyone simplify the problem and resolve it?

[#5]

Quote from: TonyPhotoplus

The other accounts are working fine with the same settings.

Presumably not /exactly/ the same settings? I'm guessing the email addresses for each of the accounts will differ?
As per my previous post, have you checked that the email address is entered correctly for the account you're having problems with? i.e. that you're not trying to send messages from an invalid or misspelt address.

[#6]

Quote

That's a fairly explicit error message and it doesn't imply it has anything to do with the password.

I really must read posts more thoroughly