Silo

Guide

Using SMTP providers

If you'd rather not use Amazon SES, Silo can send through any provider that gives you SMTP credentials. Your mail still goes out only through your account with that provider, and they bill you directly.

Before you start

  • Check that marketing email is allowed. Many providers separate transactional and marketing ("broadcast") sending, and some don't allow bulk marketing at all. Personal or office mailboxes (for example a regular Google Workspace or Microsoft 365 account) have low daily limits and are not meant for newsletters.
  • Verify your sending domain with the provider and publish the SPF and DKIM records they give you, plus a DMARC record (see the SES guide for a starting DMARC value).

Connect it

  1. In Silo, open Sending and choose SMTP (any provider).
  2. Enter the host, port, username and password from your provider. Many providers issue a separate SMTP password or API key for this; use that, not your account login.
  3. Leave Use STARTTLS on for port 587, which is what most providers recommend.
  4. Save. Silo encrypts the credentials and logs in to the server for real before accepting them, so a typo shows up now rather than on your first send.

Bounces and complaints

SMTP has no standard way to tell Silo that a message bounced or was marked as spam. Until those reports reach Silo, bounced addresses stay on your lists and keep hurting your reputation, so set this up before you send to a real list.

On the Sending page, Silo shows a private webhook URL for your account. If your provider (or a tool like Zapier) can send a webhook when a message bounces or someone complains, point it at that URL with a JSON body like this:

POST https://<your webhook URL from the Sending page>
Content-Type: application/json

{"email": "someone@example.com", "type": "bounce"}
  • type is bounce (permanent bounces only, not temporary ones) or complaint.
  • One address per request. Each report suppresses that address for your account only.
  • The URL itself is the secret. Keep it private; you can issue a new one from the Sending page at any time.

If your provider can't send webhooks, check its dashboard regularly for bounces and complaints and unsubscribe those addresses in Silo.

Troubleshooting

  • Authentication failed: confirm you're using the SMTP-specific username and password, and that the sending domain or address is verified with the provider.
  • Connection timed out: check the host and port. Try 587 with STARTTLS; some providers also offer 2525.
  • Sending stopped: if the credentials stop working later, Silo stops sending and tells you why. It never falls back to another service.