Hi CrystalMae,
There are some others who have been through this experience here -
perplexed - why is my husband getting email from questionable web sites? | Email Questions
It's impossible for me to say one way or the other with the information provided. If you reply in that discussion they might have suggestions for you too.
Also, what's your history? Is he the type? Is there anyone else that might have a reason to be making accounts with his email address to try and get him into trouble?
On the surface, everyone gets spam, that doesn't make him guilty Which email service do you use? Gmail is great and making sure the junk goes to spam.
If it's going to the inbox at a major provider that could be a sign it's email he interacts with. If he doesn't want it, why isn't it marked as spam?
What you really need is supporting evidence. Any odd billing on your credit card statements? Web browser history? Is it worth buying a
usb keyboard logger?
Since you're in his email, you could initiate a password reset at one or more of those sites using the username seen in the email or his email address "forgot username / forgot password" to find out if they're valid.
Technically you're breaking into someone else's accounts/computers if you use some of these ideas, so I can't officially recommend all of them.