SendGrid SMTP relay settings: host, apikey username, ports, limits

TL;DR: The exact SMTP settings agents get wrong: smtp.sendgrid.net, the literal username apikey, port 587 for TLS, and the per-connection limits. Plus the newline-in-pasted-key auth trap. Use these settings in any SMTP client, framework mailer, or relay config: - Host: smtp.sendgrid.net - Username: the literal string apikey. Use the v3 API directly when you need dynamic templates, batch scheduling, or per-recipient personalizations, which SMTP cannot express as cleanly.

The fix

1. Host: smtp.sendgrid.net
2. Username: the literal string apikey. Not your account email, not the key name. This is the number-one misconfiguration.
3. Password value your SendGrid API key (needs at least Mail permissions). Paste it carefully: no trailing newline or whitespace, because SMTP is line-oriented and stray linefeeds break auth.
4. Port: 587 with TLS (recommended). 25 and 2525 also work for TLS/unencrypted; 465 is for SSL. Limits: 5,000 messages per SMTP connection, and 10,000 concurrent connections from a single server. If you send bulk, reuse connections instead of opening one per message. SMTP is the right call when a framework already speaks SMTP (Django, Laravel, Rails, Flask-Mail) and you do not want an SDK. Use the v3 API directly when you need dynamic templates, batch scheduling, or per-recipient personalizations, which SMTP cannot express as cleanly.

When to use this

• This covers exactly what the title says: SendGrid SMTP relay settings.
• You are setting this up for the first time, or auditing an existing setup.
• You want the key gotchas in one place before you start.

When not to use this

• You are doing a different workflow with SendGrid; these steps are specific to the title above.
• You need the full reference docs; this is the short path, not the manual.

Compatibility

• Not pinned to a specific version; follows current SendGrid behavior.

The official SMTP integration doc gives the exact settings: host smtp.sendgrid.net, username the literal string apikey (not the key itself), password the API key, port 587 for TLS (25 and 2525 also work; 465 for SSL), plus rate limits of 5k messages per connection and 10k concurrent connections. It also warns that pasted API keys with stray newlines break auth because SMTP is line-oriented. Sources: https://github.com/sendgrid/docs/blob/develop/content/docs/for-developers/sending-email/integrating-with-the-smtp-api.md