Maybe, but this is not something Pegasus Mail has any control over.  It depends a great deal on system administration, a skill which most users do not  have.  It is better to clearly state that pmail offers no such security than to have people complaining that "Pegasus is broken" because it didn't work for them, or to engender an illusion of security.

I read in 2 posts in the FAQ that PMAIL does not offer a solution for email security on multi user setups, i.e. different users in a multi user setup can read each others emails.

I believe this statement is wrong. If the mailbox is setup in a directory in the user profile,  users will not be able to access someone else's emails. This can be done by mapping a user specific drive, e.g. H: which is located in the user profile or a home drive on a server. Theoretically it could also be setup by using the system variable  %USERPROFILE%\MyMailDirectory for the mailbox locations, but I haven't tried the latter yet.

 I would suggest to update the FAQ because email privacy can be ensured with Pegasus on multi-user systems from Win95 onwards.