User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.82 Safari/537.36

Steps to reproduce:

When creating new filters in message filtering options, I would like to use "masks" for email address and text of message.
Therefore it is not easy to filter messages containing, for example:

1 message: {G6768GgkkjhHw}
2 message: {G987ghjj86tG}
3 message: {ruyYYgn74Dg6}

because the content of each message is very different. Using the "includes {" and "includes }" options does not solve the problem, as it will also apply to all other messages containing the characters "{" and "}" regardless of the length of the string between the parentheses.

The solution could be to use the following mask:

{$$$$$$$$$$$$}

in which ~$ matches any single character.

Actual results:

Currently, it is not possible to use masking in the message filtering options, and when creating filters, you must provide specific email addresses (or the exact fragment of the address) or specific strings that the message should contain in order to be filtered.

Expected results:

It would be great to be able to use masks when specifying email addresses and message content.

I think, for example:
# would stand for any digit, that is:
sender###@gmail.com would stand for all addresses from sender000@gmail.com, sender001@gmail.com ... all the way to sender999@gmail.com.
$ could specify a single char, that is:
sender$~$@gmail.com would specify senderA5@gmail.com, senderDc@gmail.com etc...
while ~* any string of characters, so with:
sender*@gmail.com we could filter out senders from: sender01abc@gmail.com, senderABCD0123@gmail.com, etc ...

Similarly, the signs:
~#
~$
~*
could be used when creating filters based on the content of the message.

Anyway, whether the suggestion is accepted or not, I consider Thunderbird to be the best mail client in the world :)
Thank You for Your Work!

Ps. Text strikethroughs are unintentional; I did not know that using "tilde" would have this effect.

bug 363298 for regex is already on the books, which would address your situation.