What is Post SMTP Mailer plugin?
Post SMTP Mailer (formerly Postman SMTP) is a feature-rich WordPress SMTP plugin with a focus on diagnostics, security, and professional email delivery. Like WP Mail SMTP and FluentSMTP, it replaces WordPress’s unreliable PHP mail() function with a proper SMTP connection. Post SMTP’s differentiation lies in its diagnostic toolset and its mobile app companion: subscribers can install the Post SMTP Android or iOS app to monitor WordPress email delivery and receive push notifications when emails fail — without logging into WordPress.
The free version includes OAuth 2.0 authentication for Gmail and Microsoft 365 (avoiding password storage in the WordPress database), SMTP connections to any provider, email logging, a connectivity tester that diagnosises why emails are failing, and basic failure alerts. Post SMTP Pro adds advanced features including email resending, backup SMTP (automatic failover to a secondary mailer), and priority support.
For site owners who want email delivery monitoring without constant WordPress admin access — particularly for clients or managed sites — the mobile app companion is a genuinely useful differentiator. For agencies managing many client sites where email delivery issues need to be caught quickly, Post SMTP’s push notification alerts via the mobile app provide faster incident response than checking email logs manually. Its free feature set is competitive with FluentSMTP and more generous than WP Mail SMTP free, making it a strong choice for both self-managed and managed WordPress deployments.
Need Help With Post SMTP Mailer Setup, Troubleshooting, or Customization?
Need help with Post SMTP Mailer? Whether you are dealing with errors, broken functionality, styling problems, plugin conflicts, or advanced customization, we can help you fix the issue and get the plugin working properly on your WordPress site.
Get Post SMTP Mailer Expert HelpKey Features
- OAuth 2.0 authentication for Gmail and Microsoft 365 (no password stored in database)
- SMTP connection to any provider: Gmail, Outlook/Office 365, SendGrid, Mailgun, Amazon SES, Brevo, Zoho, and generic SMTP
- Email logging in free version
- Connectivity tester with detailed diagnostic output
- Mobile app (Android/iOS) with push notifications for email failures
Pros & Cons
Pros
- Mobile app with push notifications for email failures — unique monitoring capability
- OAuth 2.0 for Gmail and Microsoft 365 in free version — no passwords stored
- Email logging and connectivity tester included free
Cons
- Interface is more technical than WP Mail SMTP's setup wizard — less beginner-friendly
- Multiple simultaneous mailer connections not available without Pro
Free vs Premium
Free: SMTP configuration, OAuth 2.0, email logging, connectivity tester, failure alerts. Pro: email resending, backup SMTP/failover, priority support. Pricing at postmansmtp.com.
Common Problems & Fixes
Post SMTP connectivity tester is showing "SSL connection failed" — how do I fix this?
SSL connection failures in the Post SMTP connectivity tester indicate an issue with the SSL/TLS handshake between your WordPress server and the SMTP provider. Common causes: (1) your server’s SSL certificates or curl library is outdated — contact your host to update; (2) the encryption setting does not match the port — port 587 uses STARTTLS (not SSL), port 465 uses SSL/TLS; in Post SMTP settings, verify encryption matches port; (3) a server-level firewall is blocking outbound connections on the SMTP port — ask your host to whitelist outbound SMTP port 587 or 465.
Post SMTP mobile app is not receiving push notification alerts when emails fail — how do I set it up correctly?
Post SMTP’s mobile app uses Firebase Cloud Messaging (FCM) for push notifications. Setup: (1) install the Post SMTP app (iOS or Android) and sign in with your Post SMTP account; (2) in WordPress → Post SMTP → Settings → Notifications, enter your mobile app connection token (generated in the app); (3) run a test email failure to confirm the push notification fires. If notifications are not arriving, verify your device has Post SMTP app notifications enabled in device settings, and that the FCM token in WordPress matches the current token in the app.
Emails sent via Post SMTP are appearing in spam despite proper SMTP configuration — what additional steps should I take?
SMTP authentication is the first step; sender reputation is the second. After configuring Post SMTP: (1) verify SPF and DKIM records are in your domain DNS — check with MxToolbox SPF/DKIM lookup; (2) warm up new IP addresses gradually — avoid sending large volumes immediately from a new sending service; (3) check your SMTP provider’s domain reputation dashboard (SendGrid Reputation, Amazon SES Complaint Metrics) for any complaint or bounce spikes; (4) ensure your WordPress site is not sending spam or sending to invalid addresses — high bounce rates degrade sender reputation.
Customization & Developer Notes
How do I configure Post SMTP to use Gmail OAuth without storing my Google password in WordPress?
Post SMTP uses OAuth 2.0 for Gmail, which stores an access token rather than your password. Go to Post SMTP → Settings → Message Tab → Transport and select “Gmail API.” Follow the OAuth setup: create a Google Cloud project, enable the Gmail API, create OAuth credentials, and enter the Client ID and Client Secret in Post SMTP settings. Authorize the connection by clicking “Grant Access” which redirects to Google for authentication. After authorization, Post SMTP sends emails via Gmail API with a refresh token — your Gmail password is never stored in WordPress.
Can Post SMTP automatically retry failed emails?
Email resending (manual retry of failed emails) is available in Post SMTP Pro. In the Email Log, failed emails have a “Resend” button in Pro that retriggers the send attempt. For automatic retry on failure without manual intervention, the Backup SMTP feature (Pro) sets up an automatic failover to a secondary mailer if the primary fails — the email is retried via the backup connection without requiring manual action or admin dashboard access.
Frequently Asked Questions
Is Post SMTP free better than WP Mail SMTP free?
Post SMTP free is more generous than WP Mail SMTP free in two key areas: email logging (free in Post SMTP, Pro-only in WP Mail SMTP) and OAuth 2.0 for Gmail and Microsoft 365 (free in Post SMTP, Pro-only for Microsoft 365 in WP Mail SMTP). For users who want email logging without paying for Pro, Post SMTP free or FluentSMTP are stronger choices. WP Mail SMTP’s advantage is its more beginner-friendly setup wizard and Microsoft 365 one-click OAuth in Pro.
Does Post SMTP support Amazon SES?
Yes — Post SMTP supports Amazon SES via SMTP. Configure your Amazon SES SMTP credentials (generated in the SES console under SMTP Settings → Create SMTP Credentials) in Post SMTP’s SMTP configuration. Use the SES SMTP endpoints (e.g., email-smtp.us-east-1.amazonaws.com, port 587 with STARTTLS). Ensure your sending domain is verified in Amazon SES and your account is out of sandbox mode before sending to external recipients.
Can Post SMTP Mailer break after updates?
Yes, that can happen, especially on older sites with many plugins. This usually happens when the plugin, theme, and add-ons are updated out of sequence. In most cases, testing on staging catches the issue before it reaches the live site. From experience, backups and changelog reviews save a lot of cleanup time.
What should I check before installing Post SMTP Mailer?
Start by checking whether another plugin already does the same job. In most cases, overlap is what creates avoidable conflicts and performance issues. A common issue is installing a plugin because it looks convenient without checking the stack first. From experience, a short compatibility review avoids most of the pain later.