docs: SMTP egress troubleshooting, ISP details and unblock-request template

[vvmmaann]

What

Documentation-only PR adding operator-facing material around the SMTP outbound filter issue we surfaced via per-exit probing of the live mainnet.

Per chat discussion with the Nym team (the original community thread started by apricotastronoutskis reporting Thunderbird failures through Tech_Pundit Ashburn exits), this PR covers three of the four follow-ups that came out of the investigation:

1. A new email template for operators to send to their hoster when outbound SMTP is filtered at the network edge.
2. Updated isp-sheet.csv with notes on observed SMTP outbound behaviour for several existing entries, plus new entries for hosters with significant Nym presence not previously listed.
3. New vps-isp.mdx troubleshooting section with a step-by-step decision tree for operators encountering this issue.

Everything here is grounded in a probe of all 472 exit gateways in the current network using the official nym-socks5-client v1.1.74. Per-exit raw probe data and the probe code are kept at https://github.com/vvmmaann/nym-checker for reproducibility.

Files changed

• NEW documentation/docs/components/operators/templates/smtp_egress_unblock.md - email template, based on the wording that successfully convinced OneProvider to lift the filter on two of my own servers (Stockholm + Taipei).
• MODIFIED documentation/docs/pages/operators/community-counsel/templates.mdx - imports the new template and adds a section with short context.
• MODIFIED documentation/docs/pages/operators/troubleshooting/vps-isp.mdx - adds an "Outbound SMTP egress" section walking the operator through: test direct egress, ticket the hoster (linking to the new template), and identifying when the cause is IP reputation at the receiving mail provider rather than the hoster.
• MODIFIED documentation/docs/data/csv/isp-sheet.csv - adds SMTP outbound notes to existing entries (Flokinet, Hostinger, Linode, OVH, Mebilcom, Oneprovider, Ionos, Leaseweb, M247) and 7 new entries (HostHatch, netcup, Contabo, Hetzner, WorkTitans, xneelo, DigitalOcean).

Headline numbers from the probe

• 402 / 472 (85.2%) exit gateways are FULLY_OPEN: all four major mail providers (Gmail, Fastmail, Yandex, Outlook) reachable on port 587.
• 16 (3.4%) are PARTIAL: hoster allows SMTP, but specific receivers have flagged the IP at their own anti-abuse layer.
• 54 (11.4%) are HOSTER_BLOCKED: 0 of 4 mail providers reachable, the hoster is filtering at the network edge. These are the cases the new template targets.

The original apricotastronoutskis complaint (Tech_Pundit Ashburn, 4 nodes, all OneProvider) is in the HOSTER_BLOCKED category and would be resolved if Tech_Pundit opened the suggested ticket with their hoster.

Notes

• Methodology caveat: only port 587 was tested in this run. Port 25 (MTA-to-MTA) and port 465 (SMTPS / TLS-handshake-first) need a separate test pass; some hosters block 25 but allow 587. The CSV notes reflect this where known from public docs.
• The nym-wg-test.dev.nymte.ch test gateway operated by the Foundation itself is in the HOSTER_BLOCKED category. Worth surfacing internally.
• This PR does not change the gateway-probe pipeline. Once the testnet probe expansion lands, the categorisation here should ideally be reproducible from the Foundation's own tooling.

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