Emails sent to Gmail lost or blocked

Question

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.

Answer 1

You cannot check what is happening, GMail's spam algorithms are complex and dynamic.

The best you can do is go into your spam folder on a regular basis and flag them as 'not spam'. This will train the filter.

How effective this will be is also not predictable: it depends on the number of 'not spam' flags the filters receive, and that may be low in your case: there's nothing in your question that indicates that your mails have common properties shared with other GMail users.
Up until two months ago I had the same issues with mails sent by the BackupWordPress plugin from one of the sites I manage. I consistently kept flagging them as 'not spam' and that finally made them get through, but I may have been helped by other users of that plugin doing the same.

Answer 2

As it was said before you can't control the email quality and configuration for your clients and if you want to make sure you receive those emails here is the solution:

1. Search for supplier email
2. Click on small arrow and choose create filter option
3. Put supplier email in the TO field
4. On the next screen click on "Never send to spam"

You can also apply special labels to it or other actions.

Email from that supplier will never land in spam again.