When you receive an email, most email programs will display the sender as a name (chosen by the sender) and hide the actual email address behind it. Spam emails often abuse this by sending mails from something like 'Microsoft ([email protected])' so the name looks legit but the email address shows the fraud.
Today I received an email that my mail program (Thunderbird) said was from 'account manager (info)' so there was no actual email address visible. If I click reply Thunderbird complains that there is no valid email address.
How can I receive an email where my mail program doesn't appear to know where it is from?