If you could establish the criteria that determine whether a message is to be marked, e.g. the Subject contains xxxxx or the recipient is jane@domain.net, then you could create a filter that runs on the Sent folder and e.g. tags the sent messages with a custom tag, e.g. "Waiting For Response", with a custom color.

Thanks for the advice.

I've allready thought about a workaround like this, but I can't imagine a really working filter.

- Any change of the Subject can be seen by the recipient. - There are thousands recipients possible. - A signature like: "Waiting for your response" isn't what you want to read in a friendly email.

I declare this problem as a wish for the further developement of Thunderbird! Give us the possibility to mark an email before sending, ok?

Not sure what you're trying to achieve here; my suggestion was to provide a means of marking sent messages for your viewing, not the recipients'. But if you just want to edit the Subject or any other part of a sent or received message, there are add-ons for that purpose, e.g.:

https://addons.mozilla.org/en-us/thunderbird/addon/edit-email-subject/

https://addons.mozilla.org/en-US/thunderbird/addon/header-tools-lite/

So, you could add "Waiting for reply" to the Subject of a sent message after sending, and perhaps move the edited message to a separate folder.

Maybe the translation of "Schlagwörter" in "catchword" leads to a misunderstanding. Like i wrote in the beginning, the goal is to mark an email before(!) sending.

It's no problem to mark in the list of sent emails. But it's not useful to do so.

Clearly we have difficulty with translation here.

Two possibilities.

Tags can be used to label and categorise messages, but these are local and for your own convenience. They don't transmit along with a message.

Another is the priority flag which is part of the formal specifications of email and is represented by a standardised message header. This can be used to mark a message as important or urgent. Most email clients will honour this. Look at Options in the menu of the Compose window for this.

Show me how to add a flag, while writing an email. I hope flag is the same as "Schlagwort" in german.

Priority can't be changed later on. This doesn't help at all.

I don't think you can "while writing". You could manually tag the copy placed into your Sent folder afterwards, or you could use a filter to automatically tag it on sending.

Neither is good for an automated process, since you have no easy way to enable the tagging, or not, unless perhaps you consciously decide to use keywords in the message or subject to trigger the filter. That's what sfhowes was describing.

But the recipient won't see your tag. I don't understand if that is part of your requirements.

None of the translations given by google translate seem quite relevant:

Translations of Schlagwort

slogan Slogan, Motto, Parole, Schlagwort, Wahlspruch

catchword Schlagwort, Stichwort

catchphrase Schlagwort, Slogan

headword Stichwort, Schlagwort