Why do I get this error ‘suspicious link’?

Using HTTPS links should resolve the issue.
If you face the problem still, in that case, then it is a challenging problem to debug. The following list might contain the reason:

  1. Using the HTTP link
  2. No DKIM
  3. No SPF
  4. No DMARC
  5. Verifying your domain (click base URL) at postmaster.google.com
  6. Using public URL shorteners like bit.ly
  7. The IP pool AWS SES is using to send your emails might have a low reputation