outlook 2013 being used on two computers - one has pop3 and the other is to exchange. Both computers have primary email address set correctly but on doing a reply-all, it includes my email address and I have to manually remove. How do I avoid this?

Thx

In Exchange your primary E-mail reply address needs to be the same as the E-mail in outlook. 

Go to :Outlook\Preferences\Accounts\E-mail address and make sure that your address is correct.

This issue may happen if one of the following conditions is true:

1. Wrong Reply E-mail is set under File > Account Settings > Account Settings > More Settings > General tab.

2. For Exchange account, Outlook is using the x500 address instead of the SMTP address.

3. You have one or more contacts in Outlook for your own GAL entry and one contains the wrong address. Outlook is resolving to the copy in your Contacts, not the GAL.

In each of these situations, the From address is different than the account address so Outlook included it in the Reply to all.

Reference: http://www.slipstick.com/problems/reply-to-all-includes-my-address/

With the reply-to field being blank and have the right email address populated, the problem persists in both scenarios for my pop3 computer

For no.2, where in settings is this defined?

Google for freeware TuneReplyAll utility.