Fix SMTP Email Deliverability

We need help ensuring our transactional emails (like purchase confirmations and tracking info) reach our customers' inboxes instead of going to spam. Currently, we send these emails via a custom SMTP server.

Key requirements:
- Diagnose and fix issues causing emails to go to spam
- Ensure correct DNS settings are in place
- Handle emails with and without attachments

Ideal skills and experience:
- Expertise with custom SMTP servers
- Strong knowledge of DNS settings and email deliverability
- Experience in troubleshooting email deliverability issues