Icedove 2.0.0.24 on Lenny

[Lisi <lisi.reisz@gmail.com>]

I have recently migrated someone to a new ISP.  For this ISP his username is 
his email address with that ISP: <name>@ISP.com.  I have edited the SMTP 
settings so that he uses their SMTP server.

And now he cannot send "from" his preferred, Googlemail email address.  It has 
been changed so that his email address at the top of his sent emails is: 
<name>@ISP.com.  I have done nothing to bring about this change, other than 
change the smtp server details from his old ISP's SMTP server to his new.  
How do I reverse it?  He still wants people to use his gmail address, even 
thogh he has another SMTP server.  

What is the most baffling about this is that he was sending without a 
problem "from" his Gmail address when the SMTP server was smtp.oldISP.com.

To summarise: How can I put it right??  

Needless to say, I have clicked on every button and explored every corner in 
Icedove that I could find, and have googled.

And, if you are feeling extra generous, why did it happen?  As I say he was 
already using an email address that wasn't his ISP's.

I don't remember having a problem with this last time I set it up for him. :-/

Thanks,
Lisi