Avast Home vs McAfee Home Edition

You have to get rid of the anti-virus element of McAfee if you are using the suite including firewall. That would normally mean complete uninstall (add remove programs) reboot and custom install excluding the anti-virus element.

Or you could uninstall completely and choose another firewall, comodo (however you don’t say what your OS is and I don’t know if comodo firewall is vista compatible).

There is also a tool to remove McAfee which you should probably run after uninstalling. McAfee uninstall tool that you could run to ensure any possible remnants are removed.
http://download.mcafee.com/products/licensed/cust_support_patches/VSCleanupTool.exe

With regard to the email make sure your firewall allows ashMaiSv.exe internet access.

McAfee firewall is compatible with avast. You need to allow ashWebSv.exe to connect.
Also, avast.setup and ashMaiSv.exe should be allowed to connect for you to update and get email.

Shortly, Comodo firewall 8)

Personal Firewall Tests & Results. Firewall rating:
http://www.matousec.com/projects/windows-personal-firewall-analysis/results.php
About the leak tests limitations: http://forum.avast.com/index.php?topic=29259.msg247460#msg247460

Freeware firewalls:
http://www.firewallleaktester.com/tests_overview.php
http://www.thefreecountry.com/security/firewalls.shtml

Reviews:
XP: http://forum.avast.com/index.php?topic=27646.0
Vista: http://forum.avast.com/index.php?topic=27647.0