Questions about outbound SMTP, IPv4 allocation and BYOIP on GCP (production mail relay)

Google Cloud Compute Infrastructure
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Context: Preparing a mail‑relay on GCP. Short PoC this week (thousands/day); production MVP in October (millions/day).

Questions:

  1. Which outbound SMTP ports are blocked/restricted by default? Specifically TCP 25, 587, 465.

  2. Can the port‑25 restriction be removed project‑wide with a single request? How to request this without paid support (exact public link/form)?

  3. Fastest way to get N static external IPv4 addresses for testing/production (console/API link); default quota and how to increase it?

  4. Can GCP allocate a contiguous /28 or /24, or is BYOIP required for dedicated blocks? Typical timeline for /28 and /24 (or BYOIP)?

  5. Does GCP support BYOIP? If yes — required documents (LOA/RIR proof) and expected verification/announcement time?

  6. What information is required to approve port‑25 removal or larger IPv4 allocations? (e.g., PTR, SPF/DKIM, abuse contact, expected send volumes)

  7. Are there documented sending or rate limits that could trigger throttling/blocks? What triggers automated actions?

  8. How are abuse/complaint incidents handled and typical time to investigate/unblock IPs?

  9. Any costs/fees for port‑25 removal, static IP reservation, or BYOIP? Any limits on number of IPv4 addresses?

Thanks everyone who share some information related that questions. I’m not feeling confident with GCP and will be appreciate for any support )

Thanks,
Vladyslav