Built for transactional and bulk. The SMTP username is a literal string (the word "apikey"), not your account email. This trips up almost everyone setting it up for the first time.
Create your SendGrid API key
- Sign in at
app.sendgrid.com. - Left sidebar, Settings → API Keys.
- Click Create API Key (top-right).
- Name it (e.g. "Inflowave SMTP").
- Choose permissions:
- Restricted Access (recommended) → scroll to Mail Send → set to Full Access.
- OR Full Access if you want the same key to manage templates, suppressions, etc.
- Click Create & View.
- Copy the API key immediately - SendGrid shows it once and never again. The key starts with
SG.and is ~69 characters long.
Connect to Inflowave
- Inflowave → Settings → Email → Add sending domain → SendGrid (or Custom SMTP).
- Host:
smtp.sendgrid.net - Port:
587 - Username:
apikey(exactly this word, lowercase, no quotes) - Password: paste the SG.xxx key (no whitespace, no trailing newline - SMTP is line-oriented and a stray newline corrupts auth)
- Save, send a test.
Why "apikey"?: The SendGrid SMTP layer treats the username as a fixed identifier and authenticates entirely on the API key in the password field. The literal string is required - putting your account email there returns "535 Authentication failed".
Troubleshooting
Username is not the literal "apikey", OR the API key has a typo / extra whitespace, OR the key lacks Mail Send permission. Regenerate with Restricted Access + Mail Send Full Access.
SendGrid requires you to verify either the From email or the From domain before sending. Settings → Sender Authentication → verify the domain via DNS records.
Domain authentication (SPF + DKIM via SendGrid) is not complete. Verify the CNAME and TXT records SendGrid showed you when you added the domain.
Connection and concurrency limits
- 5,000 messages per SMTP connection. Above that, the connection is dropped and you reconnect. Inflowave reconnects automatically; you do not need to manage this.
- 10,000 concurrent SMTP connections from a single sending IP. Plenty for any single-tenant Inflowave workspace.
- Do not hardcode IPs: SendGrid rotates the IPs behind
smtp.sendgrid.netwithout notice. Always use the hostname; never lock to an IP. - Daily volume caps depend on your SendGrid plan - Free is 100/day, Essentials starts at 50,000/month, Pro and above are uncapped subject to reputation.
Official sources
- Twilio Docs - Integrating with the SMTP API (host, ports, the apikey username, per-connection cap)
- Twilio Docs - API Keys (create, restrict, revoke)
- Twilio Docs - Sender Identity Verification (the "verified Sender Identity" requirement)
- Twilio Docs - How to set up domain authentication (SPF + DKIM via CNAME)
