sasl auth LOGIN / PLAIN

[mj]

Hi,

Just a small question: we currently use posfix with sasl authentication, 
and folowing many docs, we have enabled PLAIN and LOGIN authentication.

However, googling leads me to believe that LOGIN is mostly used by 
Outlook Express, and that most (or all?) modern clients support the 
PLAIN mechanism.

I also noticed that most failed authentication attempts are done using 
LOGIN.

Now, assuming that most of these failed authentications are simply 
username/password guessing... how many problems would I expect, if I 
simply only offer PLAIN mechanism?

It's hard to find info on what clients use what auth type. So, are 
all/most modern clients capable of doing PLAIN? (thunderbird, outlook 
2010/2013) so could I simply disallow LOGIN?

MJ