If you find that email is being filtered as spam when it shouldn't be - or you suspect that email is being blocked at your email service provider because of false-positive spam detection, I recommend these steps:
Examine the contents of your junk mail folder looking for false positives and be sure to click on the "Not Spam" button, or your email's equivalent, for every message that is not spam. This "undoes" some of the things that I talked about above, and makes it less likely, though not absolutely certain, that this kind of email will be marked as spam in the future.
If you're using a desktop email program, visit your email provider's web interface if they have one and do the same. I do this regularly with Google Mail.
Add senders to your contact list or email address book. Spam filters often use these as clues to the likelihood of something being spam - if the sender is in your address book then the message is less likely to be considered spam.
If your email service or program has the ability, add the sender to a "whitelist", or set up rules that allow you to say "email from this sender should never be marked as spam".
And of course if your "security suite" is interfering with your email, turn that portion of it off - completely.
Finally - sometimes there's nothing you can do.
Some email service providers are notorious for filtering out what they consider to be spam without notification. You don't get a chance to even tell the service how wrong they are, and the sender gets no notice that their email was never delivered.
For gmail specifically they can try this. https://support.google.com/mail/answer/9008?hl=en