define sender email - depending on receipient

Let me try and understand. I think you are wanting such as this: - assuming two contacts, Joe at joe@xxx.com and Jane at jane@yyy.com - you want to write to Joe from joe-email@proton.me and to Jane from jane-email@proton.com (I'm unsure because you mention recipients, but also mention domains. - Anyway, if that is the intent, you need to see if your email host allows aliases. Some do, some don't. If yours does, you need to set up all aliases at the email host first, Then, you can click the 'manage identities' button at the account pane at 'account settings' pane. Then, when writing, click the dropdown menu on FROM line to select the desired alias.

and maybe I misunderstood. Thank you.

HI David

i can use alias - in fact, i have multiple alias setup in TB

the trouble is to find a way to create a relationship whereby

for a given recipient's domain (@receiveraa.com) : TB would automatically use aaa.email@proton.me

for another recipient's domain (@theotherb.com) : TB would automatically use bbb.email@proton.me

I hope this clarifies the concept.

I am surprise as iwould have thought this to be a common user-case, and i could not find a solution.

Mnay thanks for your attention

Well, I've been a regular here for four years and this is the first I've seen such a request. I am not aware of people using one email address for one recipient. lf there is a solution, I am unaware of it. Possibly, someone else will volunteer an approach. If there is a specific objective in doing this, such as a means to file or manage the interaction, someone here may have suggestions. I regret that my interpretation was incorrect.

I can't say I completely understand your requirement. What I get is that you want a reply to use a particular Identity based on the sender's address. Here's an add-on that might help achieve that goal:

https://addons.thunderbird.net/en-US/thunderbird/addon/folder-account/

You would first set up a filter to move a new message from a particular domain to a Folder. Then, if I understand this Add-On correctly, when you reply to a message in that folder, it will use a specific Identity.

I have no convenient way to test this, but maybe you can consider it.

3 months later...

I was really hoping that Firefox already had the feature the OP was looking for. Spark is another email client I've been using for a while, and it does have it in the form of aliases which are much easier to setup than identities. Spark automatically uses the last alias that was used to reply to the original sender. However, Spark can be a bit of a pig (sometimes it acts like classic Outlook), so I am considering Thunderbird or Mailbird as a replacement.

To sum up what I think the OP was asking for:

1. I receive an email from a recipient (like someone@somevendor.com) to my existing aliased address like myname_somevendor@mydomain.com (but it could just come to my main address at myname@mydomain.com).
2. I reply to the message after manually selecting my aliased address (Firefox calls it an identity) like the one above.
3. From then on, Firefox always auto-selects that particular aliased address (identity) each time I reply to that particular sender (the OP would like it based on the sender's domain, but I think might be happy even if it was just per sender address).