Recommendation
Try 587 STARTTLS first. If a client requires 465 TLS, use that instead — credentials stay the same pattern.
FAQ
Is port 25 available?
Outbound submission for customers uses authenticated submission ports — not open port 25 relay.
// GUIDES
587 vs 465 explained
Port 587 (STARTTLS) is the common modern default. Port 465 (implicit TLS) is also supported for clients that prefer it.