"No default mail client" message

[REDACTED]

I see this topic was discussed back in 2004, 2005, and 2008, but the issue has just come up for me now and those discussions don't resolve the problem for me. 

System:  Windows 7 Home Premium, Outlook Professional Plus 2013

Just as of yesterday (19 Nov 2014) I get this Avast! popup message every time I start Outlook and it begins downloading messages: 

"Microsoft Office Outlook
"Either there is no default mail client or the current mail client cannot fulfil the messaging request. Please run Microsoft Office Outlook and set it as the default mail client."

Neither the mail client nor the Avast! install is new (but for routine automatic updates), and Outlook most definitely is set as my default mail client in Windows.  I am running Outlook as a POP3 client, downloading my messages from GMail.  I have been doing this for years; this error message is new. 

I see the Registry entry that has been mentioned before: 
HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\PreFirstRun [containing the above error message]
but I am not finding anything in the past threads explaining why it would be running now or what I should do about it. 

[Eddy]

Import avast's certificate in Outlook and check if that solved the problem.
If not, perform a repair of avast and check.

[REDACTED]

The avast! MailScanner Root certificate is already in my Trusted Root Certification Authorities list for Windows.  What certificate is there that I could import into Outlook? 

[Asyn]

- Which Avast..? (Free/Pro/IS/Premier)
- Which version..?
- Other security related software installed..?
- Which AV(s) did you use before Avast..?

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- Which Avast..? (Free/Pro/IS/Premier)

Interesting.  As I was about to answer this post, I realized I wasn't sure; but I noticed in my mail inbox a message that just arrived today from Avast saying my Pro subscription will expire soon, and will auto-renew; so I typed "Pro" in this space, and went into the program to check the version (to respond to your next question) - and found that it was Free. 

Tracking back, I had the Free version for at least a couple of years before upgrading to Pro last December.  Apparently after I purchased Pro last December either I never fully installed it, or with some update it reverted to Free.  (Maybe when I installed and uninstalled Kaspersky; see below.)  So now I've reinstalled it, and will have to follow up on this thread when I know if the problem still exists. 

- Which version..?

FWIW, now it's 2015.10.0.2208; but until this morning it was whatever the most recent Free version was. 

- Other security related software installed..?

None that involves monitoring or intercepting traffic.

- Which AV(s) did you use before Avast..?

I had Kaspersky Internet Security installed briefly this past March, then uninstalled it and went back to Avast.  I Avast Free for a couple of years before and since (see first answer above). 

[REDACTED]

The avast! MailScanner Root certificate is already in my Trusted Root Certification Authorities list for Windows. 

How/Where did you see this in W7 ?

What certificate is there that I could import into Outlook?
The avast! MailScanner Root certificate is already in my Trusted Root Certification Authorities list for Windows

You may want to re-import and delete this per the FAQ.
...and ensure that there is no entry entitled "Avast Mail Scanner". If this entry exists, delete all certificates connected to 'Avast Mail Scanner' on the 'Servers' tab.
http://www.avast.com/faq.php?article=AVKB91

Hold down CTRL key and click on your Outlook icon to launch Outlook.......this will run it is SAFE mode (ie. no Avast add-in).
Same issue ?

Also, did you try to set within Outlook ?
http://office.microsoft.com/en-us/outlook-help/make-outlook-the-default-program-for-e-mail-contacts-and-calendar-HP010080728.aspx

Lastly, if the certificate is there then typically Outlook issues get resolved wit a clean un/re-install of Avast (see my signature for How-To).  Some people find repair does not work but the clean un/re-install does.

[REDACTED]

How/Where did you see this in W7 ?

Control Panel ->
Internet Options ->
Content ->
Certificates ->
Trusted Root Certification Authorities tab.

There is no option to remove this certificate. 

You may want to re-import and delete this per the FAQ.

That reference only discusses  Thunderbird, SeaMonkey, and The Bat clients.  To the best of my knowledge there is no function in Outlook to delete or import the .der certificate that Avast exports in accordance with the instructions on that page.  I was able to import it via Control Panel, but it did not replace or delete the "Avast Mail Scanner" one already there. 

Hold down CTRL key and click on your Outlook icon to launch Outlook.......this will run it is SAFE mode (ie. no Avast add-in).
Same issue ?

Yes. 

Also, did you try to set within Outlook ?

Yes, but unnecessary; setting it in Default Programs does precisely the same thing.  Yes, it was already set.  And as noted above, I just installed Avast Pro this morning - and the problem did not go away. 

HOWEVER, additional information: 

Further testing indicates that the error message appears not quite when I start Outlook, but when the add-on Outlook4GMail tries to sync my Outlook contacts with GMail.  That add-on was updated this week, and the reason had to do with a change in GMail itself (specifically, the Calendar API).  There may be some remaining incompatibility; the add-on is doing what it is supposed to (syncing my calendar and contacts) but seems to be generating this error.  I have now submitted a help ticket with the source of that add-on.