Can't delete system email

Question

While running Postfix on an Ubuntu, I have acquired a number of test email in an account usr1, and now I want to delete them before starting other testing. However, every time I try to delete using both d # and 'delete #`, nothing happens.

Example:

usr1@usr1:~$ mail  
"/var/mail/usr1": 5 messages 5 unread  
>U   1 usr2              Tue Apr 30 15:54  19/478   Testing local mail  
U   2 Mail Delivery Syst Tue Apr 30 15:54  78/2433  Undelivered Mail Returned to Sender
U   3 usr2               Tue Apr 30 15:55  19/614   Re: Testing local mail
U   4 usr2               Tue Apr 30 15:55  19/604   Re: Testing local mail
U   5 Mail Delivery Syst Tue Apr 30 15:55  73/2219  Undelivered Mail Returned to Sender
? d 1-5
? x

usr1@usr1:~$ mail
"/var/mail/usr1": 5 messages 5 unread
>U   1 usr2              Tue Apr 30 15:54  19/478   Testing local mail
U   2 Mail Delivery Syst Tue Apr 30 15:54  78/2433  Undelivered Mail Returned to Sender
U   3 usr2               Tue Apr 30 15:55  19/614   Re: Testing local mail
U   4 usr2               Tue Apr 30 15:55  19/604   Re: Testing local mail
U   5 Mail Delivery Syst Tue Apr 30 15:55  73/2219  Undelivered Mail Returned to Sender
? x

Can anyone explain why this is? Another Unix SE post talks about using the command as I'd expect it to work (granted, in Solaris), but I don't understand why those mails refuse to delete.

Answer 1

After much digging, I realized that the problem was that I always exited from mail using either exit or x. From the Ubuntu man page:

exit (ex or x) Effects an immediate return to the shell without modifying 
               the user's system mailbox, his mbox file, or his edit
               file in -f.

So if you're trying to delete your emails and you use d * or d 1-5, etc, you need to make sure you leave mail using either quit or q.

I hope this saves someone else my confusion.