If your domain is a G Suite/Google Apps account, the domain administrator usually has access to 24/7/365 support from Google - see https://support.google.com/a/table/3247295.
Otherwise, if some, all, or most of your emails to Gmail accounts are being classified as spam at the Gmail end, or Google are blocking your domain, or Google give a warning to the recipient, or if in some cases your mail is delayed before reaching Google at the last hop, or if (again in some cases) your mail is delayed internally at Google, you will need to comply with the Bulk Sender's Guidelines at https://support.google.com/mail/answer/81126?hl=en&vid=1-635789122382665739-3305764358.
Let’s dive into the reasons why your emails aren’t getting past the spam filters.
1. You Didn’t Get Permission to Email
2. Your IP Address Was Used for Spam
3. You Have Low Engagement Rates
4. Your Subscribers Don’t Remember You
5. You Have Low Mailbox Usage
6. Your Subject Line is Misleading
7. Your “From” Information is Inaccurate
8. You Didn’t Include Your Physical Address
9. You Didn’t Include an “Unsubscribe” Link
10. You Used Spam Trigger Words
11. Your HTML Emails Don’t Follow Best Practices
Go ahead and follow the steps to avoid emails going to spam.
