Outlook seldom sends e-mail first time

We have a client with a laptop and a desktop linked in simple peer to peer via USB. Since loading our Anti-Virus software (Command) the laptop, which is the main user machine, will almost never send an e-mail after it is composed and then “sent”. Once it has failed, however, if the e-mail is then re-sent, it virtually always goes out OK. Naturally this Irks the client considerably.
Has any one seen this phenomenae and,if so,how is it fixed to send first time, as it ought to operate??