--- title: 10.1 Outbound Mail Servers (Campaign Broadcasting) description: An Outbound Mail Server is the SMTP configuration used to deliver bulk email campaigns. When you create an email campaign, you choose which server sends… url: "https://peikly.com/docs/email-setup/" updated: "2026-10-07" category: Email tags: - Manual sync --- # 10.1 Outbound Mail Servers (Campaign Broadcasting) ## What This Feature Does An Outbound Mail Server is the SMTP configuration used to deliver bulk email campaigns. When you create an email campaign, you choose which server sends it. ## When to Use - Use when setting up email broadcasting capability for campaigns. - Do not use this for receiving replies — that requires a Reply-To Mailbox. - Do not use this for system emails (password resets, invitations) — those use a separate platform-managed server. ## Prerequisites - CompanyAdmin role. - Pro plan. - Valid SMTP credentials from your email provider. --- ## 10.1.1 Supported Providers ## Which SMTP provider should I choose? | If you are... | Best Fit | Why | | --- | --- | --- | | New to email sending | Brevo or SendGrid | Easier onboarding and clearer account setup | | Sending high volume | Amazon SES | Strong scaling and low per-message cost | | A technical team wanting flexibility | Mailgun | Strong developer tooling and domain controls | | Focused on dependable transactional-style delivery | Postmark | Strong sender quality controls and deliverability reputation | ## When should I use this vs alternatives? - Choose **Brevo** or **SendGrid** if you want the fastest path to a working sender. - Choose **Amazon SES** if cost efficiency matters more than setup simplicity. - Choose **Mailgun** if your team is comfortable with more technical configuration and diagnostics. - Choose **Postmark** if you value delivery consistency and sender reputation over marketing extras. **Generic SMTP (any provider)** Required fields: - SMTP Host (e.g., `smtp.yourprovider.com`) - SMTP Port (typically 587 for TLS, 465 for SSL, 25 for unencrypted) - Username - Password - SSL/TLS setting - From Email Address - From Display Name --- **SendGrid** Website: [https://sendgrid.com](https://sendgrid.com) Required: - API Key (from SendGrid API Keys settings) - From Email (must be a verified sender identity) - From Name - API endpoint: `smtp.sendgrid.net`, Port `587`, Username `apikey`, Password = your API key Common errors: - `535 5.7.1 Authentication failed` — API key is incorrect or not enabled for SMTP - `550 5.1.1 The email account doesn't exist` — From address not a verified sender - `403 Forbidden` — Account suspended or sender not verified --- **Brevo (formerly Sendinblue)** Website: [https://app.brevo.com](https://app.brevo.com) Required: - SMTP Key (from SMTP & API → SMTP settings) - From Email (must be a verified sender domain) - SMTP Host: `smtp-relay.brevo.com`, Port `587` Common errors: - `Authentication credentials invalid` — SMTP key not the API key; use the SMTP-specific key - Sender not authorized — verify sender email domain in Brevo --- **Mailchimp Transactional (Mandrill)** Website: [https://mandrillapp.com](https://mandrillapp.com) Required: - Mandrill API key - SMTP Host: `smtp.mandrillapp.com`, Port `587` - From Email (must be a verified sending domain) Common errors: - `535 Invalid API key` — API key is wrong or revoked - `550 Unauthenticated senders not allowed` — sender domain not verified --- **Amazon SES** Website: [https://aws.amazon.com/ses/](https://aws.amazon.com/ses/) Required: - SMTP Credentials (generated in SES Console → SMTP Settings, NOT the AWS IAM key) - SMTP Host: varies by region (e.g., `email-smtp.us-east-1.amazonaws.com`) - Port: `587` (TLS) or `465` (SSL) - From Email (verified in SES) Common errors: - `535 Authentication failed` — using IAM credentials instead of SES-specific SMTP credentials - `454 Throttling failure` — sending above your SES sending rate limit - `550 Message rejected: Email address is not verified` — From address not verified in SES - Account still in sandbox — SES sandbox only allows sending to verified addresses; request production access To request production access: SES Console → Account Dashboard → Request Production Access. --- **Mailgun** Website: [https://app.mailgun.com](https://app.mailgun.com) Required: - SMTP Login: `postmaster@yourdomain.mailgun.org` (or your domain) - SMTP Password: your Mailgun SMTP password - SMTP Host: `smtp.mailgun.org`, Port `587` - From Email (must match your Mailgun domain) Common errors: - `535 Authentication failed` — wrong SMTP login or password; check Mailgun dashboard - `550 Domain not allowed` — sending domain not verified in Mailgun --- **Postmark** Website: [https://postmarkapp.com](https://postmarkapp.com) Required: - Server API Token (acts as SMTP password) - SMTP Host: `smtp.postmarkapp.com`, Port `587` - Username: your Server API Token (same as password field) - From Email (must be a verified sender signature) Common errors: - `401 Unauthorized` — invalid API token - `422 Unprocessable Entity` — sender signature not verified; add From email as a Sender Signature in Postmark --- ## 10.1.2 Add an Outbound Mail Server 1. In the sidebar, click **Email** → **Mail Servers**. 2. Click **Add Outbound Mail Server**. 3. Fill in: - **Server Name** (internal label) - **Provider** (or Generic SMTP) - **SMTP Host**, **Port**, **Username**, **Password** - **From Email** and **From Display Name** - **SSL/TLS** setting 4. Click **Save**. ## 10.1.3 Validate a Mail Server After saving, always validate before using in a campaign: 1. On the **Outbound Mail Servers** list, click **Validate** on the server row. 2. A test email is sent to your account's email address. 3. Check your inbox for the test message. **Messages:** - `Validation email sent successfully.` — server is working. - `Validation failed: {details}` — review the error details and check credentials. - `Your account does not have a valid email address for validation.` — update your profile email first. ## 10.1.4 Linked Mailbox Warning Indicators Outbound Mail Servers can show a linked mailbox warning count when one or more Reply-To Mailboxes that use related email infrastructure are in a warning or paused sync state. Use this indicator as an investigation shortcut: - Open the affected **Outbound Mail Server** row to see whether linked mailbox warnings are present. - Then open **Reply-To Mailboxes** to find the specific mailbox showing the warning badge or paused sync badge. - The server itself may still validate successfully for campaigns even when a reply mailbox tied to the same infrastructure needs attention. ## 10.1.5 SMTP Error Code Reference | Error Code | Meaning | How to Fix | | --- | --- | --- | | `421` | Server temporarily unavailable | Retry in a few minutes; check provider status page | | `450` | Mailbox temporarily unavailable | Retry later | | `451` | Server-side processing error | Contact provider support | | `500` | Syntax error in SMTP command | Internal issue; contact support | | `535 / 5.7.1` | Authentication failed | Verify username and password; regenerate API key if provider-based | | `550 / 5.1.1` | Recipient address does not exist | Check From/To address validity | | `550 5.7.26` | Unauthenticated email not accepted (Google) | Configure SPF/DKIM on your domain | | `552 / 5.3.4` | Message too large | Reduce attachment sizes | | `554` | Transaction failed / policy rejection | Check SPF, DKIM, DMARC records; check if IP is blacklisted | --- ## Errors, Messages, and Common Fixes | Message | Why It Happens | How to Fix | | --- | --- | --- | | `Mail server not found.` | Deleted or access denied | Reload the mail servers list | | `Could not create/update/delete mail server.` | Validation or server error | Check all required fields | | `Invalid request.` | Malformed form submission | Reload the page and try again | | Linked mailbox warning count shown on a server row | One or more Reply-To Mailboxes connected to related infrastructure has sync/authentication problems | Open **Reply-To Mailboxes**, review the affected mailbox warning, and validate or reconnect that mailbox | ## What happens if this fails during a campaign? - New emails stop sending from that broadcast attempt. - Some recipients may already have received the message before the failure occurred. - The campaign remains incomplete until you fix the SMTP issue or choose a working server. - Retry only after validating the sender again. ## Best Practices - Configure **SPF**, **DKIM**, and **DMARC** records on your sending domain to improve deliverability and avoid spam filters. - Use a subdomain for sending (e.g., `mail.yourcompany.com`) to protect your main domain reputation. - Warm up new sending IPs gradually — start with small batches before large campaigns. - Monitor bounce and spam complaint rates; high rates can suspend your provider account.