I cannot receive all my emails on my mac but they are all going to my iPad. Could this be because Avast has been downloaded onto my machine?

Sorry, but your issue does not have anything to do with Apple networking. You may getter better results in obtaining solutions if you report to the MacBook area of the Apple Support Communities.

However, one thing to consider is the type of eMail account that you are using. That is, is it a POP or IMAP type account. If it is a POP account, then, by default, the first eMail client will download all of the available messages from the account. Thus, when accessing it immediately from another client the account will appear void of messages.