When the users create an account all emails go into the spam box... how can I fix this problem?

1. SMTP Settings are Correctly as guided Flynax software manual
2. DKIM, DMARC, TXT, AAAA and MX Records are Correctly
3. SMTP SETTINGS

Mail Method : SMTP
SMTP server:port - domain.com:465
SMTP server username - office@domain.com
SMTP server password - ********** (Correctly)
SMTP secure protocol - SSL