i have 2 accounts, all my family have yahoo accounts, my main one has gone weird, all my emails the ones that have been sent and incoming emails are in the inbox, which is just awful to work with, i am assuming something nasty has gotten in, have just downloaded avast, and paid for it, but no idea how to put lincense or get the license number, any help appreciated 
to start with your mail…
how do you access your mail accounts… do you go here and logg inn? http://www.yahoo.com
or do you use a mail client in your computer
what antivirus did you use before avast?
this must be uninstalled before installing avast?
then run the vendors removal tool so all conflicting files are gone
tools found here. http://singularlabs.com/uninstallers/security-software/
inserting license file
https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1084
yahoo.co.uk , it was avg but it ran out, i got the email with the license file but my computer doesnt recognise it
if you use webmail then your mail problem is not related to something in your computer
did you follow the guide i posted, how to insert license?
what error do you get?
i just clicked on the download license and says it was inserted, the mail, what can it be
i have attached a file to show you what is happening, i have cleaned out my sent box , so that cant be the problem
and no other account is like this so assumed it was some sort of virus
so your avast is working now?
you removed AVG with the tool i linked to?
contact yahoo for any questions regarding your yahoo webmail
found a number for yahoo will phone them , they are closed now
thank you