Why are only admins allowed to AUTH to lmtpd?

[Kevin P. Fleming]

I have modified my configuration here so that now my MTA (Exim 4.12) uses 
RFC2554 authentication to identify itself to lmtpd. This was done so that Exim 
could supply AUTH=<local part> on the MAIL FROM: line, thus eliminating the need 
to add "anyone p" ACLs to subfolders in order to allow direct subfolder delivery.

This is all working fine, except that I had to add my dummy authentication user 
(which I create solely for Exim to authenticate itself to lmtpd with) to the 
"admins" entry in /etc/imapd.conf. I had to do this because lmptd specifically 
allows only admins to authenticate.

Is there any particular reason why? It's not a big deal for me, but when I 
document this configuration for other people I'm sure this will raise some eyebrows.