Usually, this issue is caused by some complex spam-fighting filters on the remote server, incorrectly flagging your messages. Remote email servers have different types of SPAM protection rules for detecting which email is SPAM and which is not. Unfortunately, there is no exact resolution for this problem.
One thing you may do to resolve the problem is to ask your recipients to add your email in their address books. Most of the times this action helps and resolves the problem. However, sometimes this may be a little hard to do.
You can also create an SPF record for your domain name. The SPF record ensures that remote mail servers that do SPF checks will accept email messages from your domain only from the server which you currently use. This is important in fighting SPAM and email forgery. You can read more about SPF records at the following website:
https://www.getmailbird.com/what-spf-resources-are-available-now-that-openspf-org-is-gone/
When created, you can add the SPF record to your domain DNS zone. You can do that through your cPanel --> Domains section --> Advanced DNS Zone Editor.
Alternatively, you can can use the SPF and DKIM tools inside cPanel --> Mail section --> Email authentication and create such DNS records which may help you resolve the problem.
Setting up your email is easy when you have the right host by your side. If you need a reliable partner to help you resolve email issues and provide expert support, check out our email hosting services.