Configure Your SMTP Provider Settings in WP Postman

Everything on this page lives under WP Postman → General. Pick a delivery method from the tile grid at the top, and the panel below it swaps to show only the fields that method needs. This guide covers all eight, field by field, plus the DKIM signing accordion that applies across most of them.

Not sure which method to pick? Use WP Postman, the default. It requires the least setup, doesn’t depend on an SMTP port your host might restrict, and is the only method that reports back a real Delivered status in your logs instead of just Sent or Failed.

WP Postman (the native relay)

This is what’s selected by default whenever a WP_POSTMAN_API_KEY constant is present in wp-config.php. If that constant is missing, the plugin falls back to PHP Mail on activation so your site still attempts to send something, but nothing will actually be delivered reliably until you add the key.

Field	What it does	Guidance
From Email Address	The local part of your sending address. The domain half is fixed to your site’s own hostname and can’t be changed here, so a site at `example.com` will always send from `something@example.com`.	Safe to change anytime. `wppostman@yourdomain.com` is a reasonable default; some teams prefer `noreply@` or `hello@` depending on whether they want replies.
From Name	The display name recipients see next to the address.	Safe to change anytime. Use your site or business name, not a person’s name, unless the mail is genuinely from one person.
API key status banner	Read-only. Shows whether `WP_POSTMAN_API_KEY` is currently defined in `wp-config.php`.	Not editable from the dashboard by design. Add the constant yourself: `define('WP_POSTMAN_API_KEY', 'your-key-here');`, placed above the line that reads `/* That's all, stop editing! */`.
Auto DKIM Signing	A live DNS check, not a setting. Queries a public DNS resolver for a TXT record at `_mb.yourdomain.com` and reports whether it’s present.	Nothing to configure. If the badge reads Not Configured, your domain either isn’t using WP Stratos DNS yet or the record hasn’t propagated. See DNS Configuration or contact support if it’s been more than a few hours.

The API key is deliberately kept out of the database and out of the settings form. Storing send credentials as a wp-config.php constant instead of a WordPress option means the key survives a database import or a site clone without landing somewhere it shouldn’t, and it can’t be read back out through the REST API or an exported options table.

PHP Mail

No fields. Selecting this tells WordPress to fall back to its original behavior and hand mail directly to the server’s local mail() binary.

Treat this as a diagnostic fallback, not a real delivery option. It carries no SPF, DKIM, or DMARC authentication of any kind, and most consumer inbox providers either bulk-file or silently drop mail sent this way. Its only legitimate use is confirming that WordPress itself is calling wp_mail() correctly while you troubleshoot something unrelated to delivery.

SMTP.com

Routes mail through a dedicated SMTP.com relay connection on port 2525, useful if your organization already runs mail through SMTP.com for other properties.

Field	What it does	Guidance
From Email	Sender address shown to recipients.	Safe to change anytime.
From Name	Sender display name.	Safe to change anytime.
Sender Name (SMTP.com username)	Your SMTP.com account’s sender identity, used as the SMTP username.	Comes from your SMTP.com dashboard under sender management, not something to invent.
API Key	Your SMTP.com API key, used as the SMTP password.	Rotate immediately if it’s ever exposed. Test a send right after changing it, since a stale or revoked key fails silently until the next send attempt.

Brevo

Connects over SMTP to smtp-relay.brevo.com. Brevo was formerly known as Sendinblue, and some older documentation and dashboard screens may still use that name.

Field	What it does	Guidance
From Email (also used as SMTP username)	This single field does double duty: it’s both the sender address recipients see and the SMTP login.	Must be a sender address you’ve verified inside Brevo, not just any address on your domain. Unverified senders get rejected at the SMTP layer.
API Key / SMTP Password	Brevo’s SMTP key, specifically.	This is not the same string as Brevo’s general-purpose API key. Brevo issues both from separate screens under SMTP & API in their dashboard, grab the one labeled for SMTP or the connection will authenticate-fail even with an otherwise correct key.

Mailgun

Connects over SMTP, with the host chosen automatically based on your account’s region.

Field	What it does	Guidance
From Email	Sender address.	Safe to change anytime, but must be on a domain verified in Mailgun.
From Name	Sender display name.	Safe to change anytime.
Domain	The sending domain configured in your Mailgun account, used as the SMTP username.	Copy exactly from Mailgun’s domain list, subdomains matter here.
API Key	Your Mailgun SMTP password (not your Mailgun API key, despite the label). Find it under the domain’s SMTP credentials panel in Mailgun.	Test a send after entering it. A mismatched region setting (below) will fail authentication even with a correct key.
Region	Switches the SMTP host between `smtp.mailgun.org` (US) and `smtp.eu.mailgun.org` (EU).	Requires testing after any change. Mailgun’s US and EU infrastructure are fully separate; picking the wrong region against a domain provisioned in the other one fails every send until corrected.

SendGrid

Connects over SMTP to smtp.sendgrid.net. SendGrid’s SMTP username is always the literal string apikey, which WP Postman sets automatically, so there’s no username field here.

Field	What it does	Guidance
From Email	Sender address.	Must be a verified sender or verified domain in SendGrid, otherwise every message is rejected regardless of how correct the API key is.
From Name	Sender display name.	Safe to change anytime.
API Key	A SendGrid API key with at least Mail Send permission.	Scope it narrowly. A key with only Mail Send access limits the blast radius if it’s ever leaked, compared to a full-access key.

Gmail

Connects over SMTP to smtp.gmail.com. The field names reference OAuth, but the actual authentication is standard SMTP AUTH using a Google App Password, not a full OAuth consent flow. Don’t go looking for a “Sign in with Google” button, there isn’t one.

Field	What it does	Guidance
Gmail Address	The Gmail or Google Workspace address recipients see as the sender.	Must match the account the app password below was generated on.
From Name	Sender display name.	Safe to change anytime.
OAuth User Email	The SMTP username, functionally identical to the Gmail Address field above.	Keep it in sync with Gmail Address to avoid a confusing authentication mismatch.
Client Secret / App Password	A 16-character Google App Password, generated after enabling 2-Step Verification on the account.	Requires testing after every regeneration. Google App Passwords can be revoked from the account’s security settings at any time without notice to this plugin.
Encryption	TLS or SSL.	Leave on TLS unless you have a specific reason to change it.
SMTP Port	Defaults to 587.	587 with TLS is standard. Only change this if Google’s documentation for your account type says otherwise.

Google enforces a rolling daily send cap on personal and Workspace accounts, commonly cited around 500 messages per 24 hours for personal Gmail and higher but still capped limits for Workspace. That ceiling makes this method unsuitable for any site sending real transactional volume, order confirmations, password resets, form notifications, all counted together. Reserve it for staging sites, internal tools, or genuinely low-traffic personal projects.

Other SMTP

The generic connector. Use this for any provider without a dedicated panel above, including Amazon SES, Postmark, or a private mail server.

Field	What it does	Guidance
From Email	Sender address.	Must match a domain or address your chosen provider allows you to send as.
From Name	Sender display name.	Safe to change anytime.
SMTP Host	Your provider’s SMTP hostname.	Copy exactly from provider documentation. Amazon SES hosts are region-specific, for example `email-smtp.us-east-1.amazonaws.com`, and won’t work if the region doesn’t match where you verified your sending identity.
SMTP Port	Common values: 587 (TLS), 465 (SSL), 25 (rarely usable, frequently blocked by hosts).	Requires testing after any change. Start with 587 unless your provider specifically directs otherwise.
Encryption	TLS, SSL, or None.	Requires testing after any change. Must match what the host and port combination actually expects, a mismatch here produces a handshake failure that looks identical to a wrong password in the logs.
SMTP Authentication	Whether the connection requires a username and password.	Leave enabled. Virtually no production SMTP provider accepts unauthenticated connections anymore.
Username	Your SMTP login.	Provider-specific. For Amazon SES this is a generated SMTP username, not your AWS access key ID.
Password	Your SMTP password.	Same note as above, this is a dedicated SMTP credential for most providers, not your account’s main password or API key.
Auto TLS	Lets PHPMailer opportunistically upgrade to TLS if the server offers it, even when Encryption is set to None.	Safe to leave enabled. It only upgrades the connection, it never downgrades a connection you’ve explicitly set to TLS or SSL.

Manual DKIM signing

This accordion sits below the delivery method panels and applies regardless of which method you’ve selected, with one exception: it has no effect on PHP Mail, since that path bypasses PHPMailer’s signing capability entirely. Everything else, including the native WP Postman relay, gets signed if you fill this in and enable it. This is a separate mechanism from the Auto DKIM check described in the WP Postman relay section above. That one verifies a record WP Stratos manages for you automatically. This one signs outgoing mail with a key you generate and control yourself, useful if you need DKIM under your own domain’s DNS rather than WP Stratos’s.

Field	What it does	Guidance
Enable DKIM Signing	Master switch for this section.	Requires testing after enabling. A misconfigured key doesn’t block sending, it just signs with a broken signature, which some receiving servers treat as worse than no signature at all.
Domain	The domain your DKIM key is published for.	Must exactly match the `d=` domain your DNS TXT record uses.
Selector	The DKIM selector, the string that appears before `._domainkey` in your DNS record name.	Must exactly match what’s published in DNS. A mismatched selector fails silently at the receiving end, your mail sends fine but the signature never validates.
Private Key (PEM)	Your DKIM private key, pasted in full including the `-----BEGIN` and `-----END` lines.	Generate this alongside your DNS TXT record, most DNS or email providers walk you through both together. Never share this value outside your own infrastructure.

Publish the matching public key as a DNS TXT record before enabling this. Signing mail with a key that has no published counterpart doesn’t just fail to help, it can actively hurt: some spam filters flag a DKIM signature that doesn’t validate more harshly than a message with no DKIM signature at all.

Testing a change

Every field change is saved with the Save Changes button at the bottom of the General tab. After saving, confirm it actually works before moving on:

Open the Test Email tab

Go to Settings → WP Postman → Test Email.

Send to an inbox you can check immediately

Fill in a recipient you have access to right now, not an address you’ll check later. The subject and message fields come pre-filled, you can send them as-is.

Read the result banner

A success or failure notice appears at the top of the page immediately. Failures for the native relay method point you to the Debug Log tab for the full API response. Failures for SMTP-based methods show the SMTP error directly in the banner.

Check the Mail Log entry

Open Mail Log and confirm the attempt shows the status and delivery method you expected. This is also where you’ll catch a message that reports Sent but never actually arrives, worth a look even on a successful test.

Do this after every field change, not just after switching delivery methods entirely. A single wrong character in an API key produces a save that looks completely normal until the next real send fails.

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Configure Your SMTP Provider Settings in WP Postman

WP Postman (the native relay)

PHP Mail

SMTP.com

Brevo

Mailgun

SendGrid

Gmail

Other SMTP

Manual DKIM signing

Testing a change

​WP Postman (the native relay)

​PHP Mail

​SMTP.com

​Brevo

​Mailgun

​SendGrid

​Gmail

​Other SMTP

​Manual DKIM signing

​Testing a change

WP Postman (the native relay)

PHP Mail

SMTP.com

Brevo

Mailgun

SendGrid

Gmail

Other SMTP

Manual DKIM signing

Testing a change