it worked at one place ... but for some other lines it didn't.
Find[! \@]{1,}\@[!.]{1,}.[a-zA-Z]{3})([!. ])
Replace with: \1 \2

For Example: ognjanovic@collegeclub.comA -changed to- ognjanovic@collegeclub.com A (perfect)

but not for these lines:
oni@optonline.netPortage
pollonais@collegeclub.comPALM
pappyjump@aol.com HoustonTX (where single space is already there)
orit.moalem@adttsa.com Petaluma
randall.e@aug.comGlen
otutmaz@aol.comElmhurst