Well I use my own sendmail.cf, compiled from the supplied sample files, with changes to block the unacceptable promiscuous relay feature etc, which has been an open relay since time epoch with AIX ;-(, add relay for SMTP after POP3 authentication and name mapping features etc..
My aliases files are in /etc, with a .dir and .pag there too, I have various files of my own requirements for in and out bound name mappings in /etc/mail.
All my files are root.system 644 permissions in /etc, and 640 for those natively used in /etc/mail. (I have links from /etc to /etc/mail for those natively in /etc.) The /etc/mail directory is 750 root.system, /etc and / 755.
When I edit one of my name mapping files I run:
makemap dbm virtusers < virtusers # for example
And I run
sendmail -bi
if my aliases have changed
(actually I have a script to do this based on the timestamps).
My sendmail.cf refers to /etc/aliases, not /etc/mail/aliases.
So I suggest, first check what your sendmail.cf (supplied ?) file says as to which directory it's looking in, and then check the permissions on those directories as well as the files themselves.
In any event, nobody should use the supplied AIX sendmail.cf as that is clearly an accident waiting to happen, you should compile your own after setting your required features and in particular removing the incredible open relay ! Oh and do not copy a sendmail.cf from another system unless you have a compiled generic file suitable for such use - use only the supplied sample source files to compile a suitable file.
If anyone would like more advice on how to do all these good things, essential for any virtual name hosting, for a small fee which will go towards running this site, I am sure I can be persuaded to part with the sum total of years of accumulated grief on the subject
