[horde] only RSET accepted now

[Twilek]

> RSET is the SMTP reset command. No idea why your server thinks it    
> >should only be sent such a command. Perhaps your message is above  
> the   >message_size_limit, or some other part of your stack is  
> failing due to   >the size?  I checked the exim config. I have not  
> set a size limit, so it should be at 50 MB by default.  But the  
> error triggers way below that. I cannot really pinpoint when the  
> error started (maybe it was an exim update). I use exim version 4.88  
> (debian package). The source file which generates  the error    
> "smtp_in.c" has seen some commits in the last months. Maybe some  
> subtle behaviour  change of exim has been introduced.  Regards   
> Henning