Are you having problems with some important emails being detected as spam? Not to worry please see this explanation.
The Gmail system considers a number of factors when classifying messages as spam. To best protect our users, we can't share specific details about our spam filters. Google's Spam filters are designed to respond to user preferences at scale. Please note that our spam engine learns overtime and results are often not immediate. However, there are certain steps you could take to make it less likely that these messages will be marked as spam and to also improve a sending domain’s spam reputation over time.
-Add the sending domain or the sender email address to your domain’s Approved Senders list as per the steps in this Help Center article https://support.google.com/a/
-Add the sending IP or IP range used by the sending domain to your domain’s whitelist - you can find the full steps for updating your whitelist in this Help Center article https://support.google.com/a/
-Mark the message as not Spam in Gmail by clicking 'Not spam'. After marking a few messages as ‘Not spam’, this will train the Gmail spam filter over time that these emails should no longer be marked as spam. See https://support.google.com/
-Help the sender follow Bulk Sender Guidelines. If you know the sender in question, please request that they make the following changes per Gmail's Bulk Sender Guidelines in the Help Center at https://support.google.com/