HandShake Invoicing sends emails using WordPress’s built-in wp_mail() function. On most shared hosting environments this uses PHP’s mail(), which is unreliable — emails may land in spam or fail silently.

For reliable delivery, connect wp_mail() to a dedicated sending service using an SMTP plugin.

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Recommended setup

Step 1 — Install an SMTP plugin

FluentSMTP is free, lightweight, and works well with HandShake Invoicing.

Step 2 — Create a free sending account

Any of these services work on the free tier for low invoice volumes:

Service	Free tier
Brevo	300 emails/day
Mailgun	1,000 emails/month for 3 months
Postmark	100 emails/month free
Resend	3,000 emails/month free

Step 3 — Connect FluentSMTP to your sending service

Follow the setup wizard in FluentSMTP. Once connected, all wp_mail() calls — including invoice emails — will route through your sending service.

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Checking delivery status

The Last sent column on the Invoices page shows whether the last email attempt succeeded or failed, and how long ago it was sent. A ✗ Failed status means wp_mail() returned false — usually a configuration issue with your SMTP setup.

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Sender name and address

The sender name is your WordPress site name (Settings → General → Site Title). The sender email is your WordPress admin email (Settings → General → Administration Email Address).

Your SMTP provider may require the sender email to match a verified domain or address. Check your provider’s documentation if emails are not delivering.