It appears to me that you are trying to send from the info@en* account through the nssood@en* smtp server, instead of the info@en* smtp server. Open Tools/Account Settings, select the info account in the left pane, then look at Outgoing Server (SMTP) in the lower right pane. Some mail providers, such as gmail, enforce 'ownership' between the sending account and the sending server.

Hmmm. My problem does seem similar if not exactly the same - see description, below.

So is my mail provider rejecting my other return email addresses because it is not the "official" one connected to my account? I don't get it when I am only using the return email address when sending through my provider's system.

Is there any way around this?

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I am having an irritating Thunderbird problem that I can’t figure out how to fix. Any suggestions would be appreciated. In the past I have used different email addresses – for different purposes as my return email address. I would just click on the dropdown and I would then click on the one I wanted to use and then send the email – no problem. Of the three return email addresses only one of them was the same address that appears as my account name address that appears when I open “Account Settings.” In “Account Settings” I use one of my alternative email addresses in both “email address” and “reply-to address.” Recently, when I try to use one of the other two email addresses, and I click “send” I am getting the following message:

An error occurred when sending mail. The mail server responded you are not authorized to send mail as: [email protected]. Please verify that your email address is correct in your account settings and try again.

When I then switch to using my account settings name address the email is accepted.

So what can I do to allow me to use all three email addresses at any point?

The simplest approach is to have all addresses set up as separate accounts, and to create separate smtp servers for each one, and to specify that account A uses smtp server A, account B uses smtp server B etc. Separate identities attached to an account are possible, but this is not feasible with some providers such as Gmail or Google-supported domains.

I have 2 accounts set up in Thunderbird. However, irrespective of number of accounts set up, Thunderbird uses a single outgoing server. The server could be the same for any outgoing email from any account. Incoming server needs separate authentication (password) for each email account. I never had this problem with thunderbird before.

Yes, some people manage to send from all their accounts through a single, default server. Some services, such as Gmail, let you add non-gmail accounts to the principal Gmail account as valid addresses from which to send through the gmail smtp server. The method I recommended will work in all situations.

The toc.santos account is sent by the smtp toc server.