In the past I could always use the following email addresses interchangeably

[log in to unmask]
[log in to unmask]


Now suddenly posts that use the address 
[log in to unmask]

are sent back to me with this comment:


  ----- The following addresses had permanent fatal errors -----
<[log in to unmask]>
   (reason: 550 5.0.0 <[log in to unmask]>... No "nisus" in name directory)
(…)


The address <[log in to unmask]> still seems to work, BUT *replying* to a message is not possible, because the Reply-To field still carries the address <[log in to unmask]>. In other words, one has to EDIT the mail and replace *manually* the automatically inserted [log in to unmask] with <[log in to unmask]>.


Has anyone else noticed this? What is happening here?


Þorvarður