(user@domain.invalid wrote several articles)


assuming the EMail address is not intended, ans assuming your web browser is
Mozilla-like, you could try this:

Enter "about:config" (for advanced users) in the URL field
Then look for strings containing "useremail", like
"mail.identity.id2.useremail". You can double-click on the line and enter a
new value (= EMail address) there.
Otherwise the address might be available in mail application's Account
Settings (right mouse button over mailbox). Specifically compare "Account
Name" with "Email Address"

Sorry for this off-topic,