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Adding Fastmail Addresses to Thunderbird

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I can set up accounts for addresses set up with my ISP and with Gmail in Thunderbird, but I cannot set them up for Fastmail addresses.

In exchanges with Fastmail, they showed me screenshots with such email addresses set up. The only way I know to have Thunderbird use any email address is to set up an account in Thunderbird for that address which requires validating the account set up with the email address provider's domain. If I understand Fastmail correctly, that cannot be done. Instead, they say I can set them up as identities (if I understand them correctly) but I don't know how to do that without accounts in Thunderbird.

If anyone has successfully set up multiple @fastmail.com email addresses in Thunderbird, I'd like to know how it was done.

I can set up accounts for addresses set up with my ISP and with Gmail in Thunderbird, but I cannot set them up for Fastmail addresses. In exchanges with Fastmail, they showed me screenshots with such email addresses set up. The only way I know to have Thunderbird use any email address is to set up an account in Thunderbird for that address which requires validating the account set up with the email address provider's domain. If I understand Fastmail correctly, that cannot be done. Instead, they say I can set them up as identities (if I understand them correctly) but I don't know how to do that without accounts in Thunderbird. If anyone has successfully set up multiple @fastmail.com email addresses in Thunderbird, I'd like to know how it was done.

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Unless you are using custom domains, xxxx@fastmail.com should configure automatically just fine.

If you have custom domains, just use port settings recommended by fastmail as they should have documented on their website - no?

See also https://support.mozilla.org/en-US/kb/configuration-options-accounts

Please post your results.

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Thanks, Merv.

Can you (or anyone) tell me how the password used when setting up an account in Thunderbird is used in the setup process?

When adding an account, after entering name, email address and password, there is a validation step. I have always thought that this step did a few simple things: 1) verify that the address does not already exist and post a message if it does 2) send the information to the named domain's email server and - possibly - validate that the referenced domain has an account with that name set up If unsuccessful in any particular a message is returned. Is this what actually happens? Is the password used at all in this step?

After passing those validations, the next step is to choose mail protocols for inbound and outbound mail and connection validations for port numbers and security protocols. After making those choices and clicking the Done icon, there is a further verification process. During this process a message stating that the password is being validated is flashed. I have always thought that in this step a message is sent to the named domain's server where the domain's software checks and validates the port number and security settings and the password and returns a message indicating success or failure which Thunderbird then interprets and displays an appropriate message.

Is this what actually happens or do I need an education?

I keep getting an error at this step. FWIW, I choose to use POP3 and accept the suggested port numbers and security options. I've looked up Fastmail's settings information and found the suggested values to be those that Fastmail publishes.

Here, I think, is the rub. From responses from Fastmail support, I think there are only ever 2 passwords used by Fastmail regardless of how many user email addresses are setup in Fastmail. There is what they call an 'app password' which must be set up to allow Thunderbird to access Fastmail, and there is a single password that is set up with the mail Fastmail account/user email. This second password is the only one Fastmail checks when processing email messages. It is quite possible that I do not understand this correctly.

In any case, if my understanding as stated above is correct, then the question becomes, "What password should be used when setting up Fastmail domain email addresses in Thunderbird?"

I have tried using the app password without success. I have tried using the 'master' email password without success. I've tried using a password generated by Roboform without success, although this doesn't surprise me in the context of my understanding of the process because I cannot set up separate passwords for separate Fastmail email user addresses.

In every case I get the error message shown in the attached screenshot, regardless of password used. The message doesn't say specifically that the error was a password validation failure or that the settings are wrong.

Finally, I CAN and HAVE successfully an account in Thunderbird for my Fastmail Account/User email address. This addy works, as best I can tell. I would greatly appreciate someone correcting my misunderstanding or adding more insight into the process.

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Have you created an app password for Thunderbird? If not create one now.

Try and configure your account using the app password as the password in the account setup.

Fundamentally the program attempts to log into the fastmail account at the point of verification and get various parameters from the server such as it's capabilities in the case of IMAP. So you must be using the password that is allowed for Thunderbird that was created before you tried to create the account.

It is possible to manually connect to a mail server using a command line utility in the operating system and attempt to log in just as Thunderbird does. You might also want to ensure that all references to the account have been removed before you try again. (password manager and delete any passwords saved and account manager and make sure you have no non working account already added.