Cybexsoft SMTP

WordPress sends mail with PHP’s mail() function by default, which many hosts throttle or block outright — so the message never arrives and nothing on the site says so.

This plugin replaces that transport and then keeps working after the swap, which is the part most setups leave out:

• Several mailers at once, with roles. Add as many as you like and say which one sends. Pro adds a backup that takes over automatically when the primary starts refusing mail.
• Nothing is silently lost. A send that fails is held and retried on a widening schedule instead of disappearing, and sending pauses while a mailer is plainly broken rather than throwing every message at it.
• A connection trace, step by step. Watch the handshake with your mail server or API key and see exactly which step fails, instead of reading “could not send”.
• Deliverability diagnostics that tell you what to publish. SPF, DKIM and DMARC checked against your sending domain, with the record found, what it means, and the exact change to make.

New in 1.1

• Failure alerts in Slack or your own webhook, with an all-clear once mail goes out again
• Sending limits per mailer, so a provider’s hourly or daily cap delays mail instead of refusing it
• A dashboard widget, multisite network settings, SparkPost, an optional log preview with one-click retry, WP-CLI commands and a read-only REST API
• In Pro: routing rules that send some mail through a different mailer, and Mandrill and SMTP.com

Free features

• Mailers: generic SMTP, Amazon SES (via SMTP), SendGrid, Mailgun, Brevo, SMTP2GO, SparkPost (US or EU), or default PHP mail — set up as many as you like and choose which one sends
• Email log with search, status filter, and CSV export — kept indefinitely, and showing which plugin or theme sent each message, with an optional short text preview and one-click retry of failed mail
• Held mail: a message whose send fails is kept and retried on a widening schedule instead of being lost
• Sending limits per mailer (a minute, an hour, a day), with ready-made figures for the SES sandbox, Gmail and shared hosting: mail past a limit waits in the queue instead of being refused
• A WordPress dashboard widget: whether mail is going out, the last 7 days sent and failed, and anything waiting
• Multisite: set the mailer once in Network Admin for every site, let sites choose their own if you like, and see each site’s sending and email log from one screen
• Domain diagnostics: SPF, DKIM and DMARC record checks
• Send test emails and trace the connection to your mailer step by step, with a rolling debug log for failures
• Force-from controls so other plugins can’t silently change your From address
• Allow & block lists: never email a blocked address or domain again
• Failure alerts: an email to you once sending starts failing, at a threshold you set — and to Slack or a webhook of your own, with an all-clear when sending works again
• Credentials encrypted at rest, or supplied from wp-config.php and kept out of the database entirely
• A read-only REST API for your own dashboards: sending stats and the email log, for administrators signing in with an application password
• WP-CLI commands for status, test email, the retry queue, the email log, DNS checks, settings export/import and the access lists — each exits non-zero when something is wrong, for monitoring

Cybexsoft SMTP Pro is a companion plugin you install alongside this one. It adds its features to the same settings screen, so there is still only one place to configure anything. It is free during early access: ask us and we will email you the download and a license key. It adds:

• Open & click tracking
• Automatic blocking of addresses that keep bouncing, and an allow-list-only mode that stops a staging site emailing real customers
• Backup mailer with automatic failover
• Richer failure alerts: several recipients, your own counting window and quiet period, any number of alert channels including Microsoft Teams and Discord, and no alarm for a message the backup mailer already rescued
• Postmark, Resend, MailerSend, Mailjet, Elastic Email, Zoho ZeptoMail, Mandrill and SMTP.com mailers, plus Gmail & Outlook over OAuth
• Automatic log pruning on a retention window you set, plus a full content archive
• Weekly deliverability reports

External services

This plugin can connect to the external services listed below. Sending email
necessarily involves handing your message to a mail provider, so the mailer
you choose is the main one — but the plugin only ever talks to the provider
you configured, using credentials you supplied. Everything else here is
optional and off until you act.

The mailer you configure

The plugin sends your outgoing WordPress email through whichever mailer you
select under Settings. Six of the free mailers are third-party services of
their own: five HTTP APIs and Amazon SES. In each case what is sent is the
outgoing message — recipients, subject, body, attachments and headers —
together with the credential you configured, and only while that mailer is the
selected one:

• SendGrid — sent to https://api.sendgrid.com. Service provided by
  Twilio SendGrid: terms of service,
  privacy policy.
• Mailgun — sent to your configured Mailgun API host. Service provided by
  Mailgun: terms of service,
  privacy policy.
• Brevo — sent to https://api.brevo.com. Service provided by Brevo:
  terms of service,
  privacy policy.
• SMTP2GO — sent to https://api.smtp2go.com. Service provided by
  SMTP2GO: terms of service,
  privacy policy.
• SparkPost — sent to https://api.sparkpost.com, or
  https://api.eu.sparkpost.com for an EU account. Service provided by
  Bird (SparkPost): terms of service,
  privacy policy.
• Amazon SES — sent over SMTP to email-smtp.<region>.amazonaws.com, for
  the AWS region you select in the settings. What is sent is the outgoing
  message, authenticated with the SES SMTP username and password you
  configured, and only while Amazon SES is the selected mailer. Service
  provided by Amazon Web Services:
  service terms,
  privacy notice.

The remaining free mailers — generic SMTP and PHP mail — connect to the mail
server you name in the settings, not to a service of ours. The Tools tab’s
connection trace opens a connection to that same server and stops before any
message is sent.

For SendGrid and Mailgun, that same connection trace instead checks your key
against the provider without sending any message: it requests
https://api.sendgrid.com/v3/scopes with your API key, or
https://api.mailgun.net (or api.eu.mailgun.net on the EU region) with your
API key and the sending domain you configured. It runs only when you click it,
and nothing else about your site is sent.

Cybexsoft licence server

Used only once you have entered a Pro licence key under Cybexsoft SMTP → License.

Your licence key, your site’s home URL, and the product and version being
licensed are sent to https://cybexsoft.com/api/licenses/verify when a key is
activated and periodically thereafter to confirm it is still valid, and to
https://cybexsoft.com/api/licenses/deactivate when a key is removed. Nothing
is sent while no licence key is stored, and the free plugin never contacts
these addresses at all — they are used only by the Pro add-on.

Service provided by Cybexsoft: terms of service,
privacy policy.

Alert channels (Slack, Microsoft Teams, Discord, your own webhook)

Used only if you add an alert channel on the failure-alert card in Settings.

When an alert goes out, when sending works again, and when you press “Send
test alert”, the plugin posts a short JSON message to the webhook URL you
entered: your site’s name and address, what happened, how many messages
failed, the first error the mail server gave (which can include a recipient’s
email address), the mailer in use, the times, and a link to the email log.
Nothing is sent to any channel you have not set up, and nothing is sent
otherwise.

• Slack (hooks.slack.com): terms of service, privacy policy.
• Microsoft Teams, through a Power Automate workflow URL: terms of service, privacy statement. Cybexsoft SMTP Pro only.
• Discord (discord.com): terms of service, privacy policy. Cybexsoft SMTP Pro only.
• A webhook address of your own goes to whichever service you chose; its terms are its own.

“Get Pro for Free” request form

Used only if you open that form and submit it.

The name, email address, website and message you type, are emailed to
admin@cybexsoft.com so we can send you the Pro download and a licence key. The
request is sent through this plugin’s own mailer — it is an ordinary email,
not a background call — and if your site cannot send mail yet, the form offers
to open the same request in your own email application instead.

Deactivation feedback

Used only if you choose a reason in the dialog shown when you deactivate the
plugin. The dialog can be skipped, and skipping it sends nothing; deactivation
proceeds either way.

If you do submit a reason, your site’s URL, the plugin version and build, the
mailer you had configured, the reason you picked and any note you wrote are
emailed to admin@cybexsoft.com.

showdns.net

The Deliverability tab links out to https://showdns.net, which runs the same
SPF, DKIM and DMARC checks from outside your server. The plugin makes no
request to it — nothing is sent unless you click the link, at which point your
browser visits it like any other site and the domain being checked appears in
the URL.

Service provided by Cybexsoft: privacy policy.