We have seen complaints on a number of forums about this issue.  We can not confirm or deny that there is a problem, but we have long advised clients to avoid the free email accounts, for credibility issues if nothing else.  Many online sellers, payment agents etc will not use any of these accounts for transactions.  If you are doing any type of online business using these types of accounts be aware that many transactions will be killed if they are linked to these types of accounts.

Most online banking, credit cards companies and even Paypal are not restricting these accounts due to issues of identity verification and security.

These post may help you with more information.  We are providing them for information purposes, and can not attest to their validity.

We strongly encourage our clients to use domain based email accounts, or those provided by you internet service provider.

See these for more:

http://answers.yahoo.com/question/index?qid=20090127070938AAWBwN1

http://www.realfreewebsites.com/blog/dropped-emails-yahoos-gain/

http://hubpages.com/hub/Hotmail_Fails_To_Deliver_Up_To_81_Of_All_Attachment_Emails