I'm sending emails from my own domain, that are relayed by my local ISP. Recently, I discovered that some of my emails are blocked by Gmail or marked as spam, and this is happening since months.
So I sent an email containing subject "Test" and body "Test email", and this one has been received correctly by Gmail, in my inbox.
But when I forward an email from a supplier, with 2 PDF files attached, to another supplier using Gmail (and setting my personal Gmail address in cc), the email is simply never received. Neither in the inbox, nor in the spam folder.
Some weeks ago, these kind of emails went to the Gmail spam folder.
How can I check what is happening, and how can I solve this ?
Note: only Gmail has this behavior. All other recipients I send emails to, on various domains, always get my messages.