@me.com

No, both icloud and me domains work fine. That is not the issue. The possible issues can be:

• Your assigned public IP Address is flagged as being a source of spam. This is an issue only your ISP can fix. But in your OP you said the problem does not happen all the time so this is likely not your issue.
• Your recipients have flagged your emails as spam. Only they can change the behavior of their email client rules.
• You are including content in your emails that the recipient's email provider is flagging as spam. Try to find the offending content and change it.
• Your recipients have miss-configured their email clients.
• Your recipients are not checking their spam folder for valid email incorrectly routed to spam. If this is the case the recipients need to "teach" their email client that your emails are not spam.

The recipient will have to configure their email client to not put your emails into spam.

I use several Windows computers and receive email from me.com addresses almost daily without issue. The issue is likely a setting on the recipient's end.