SMTP and Sending
Invoice sending and custom SMTP
Send invoices with default delivery or your own SMTP setup.
Updated: 2026-02-18
Before you start
- Invoice settings configured
- Sender email address and mailbox credentials available
Open related features
Layered workflow
Layer 1: Channel selection
- Default sending (via Resend) works immediately with no configuration.
- Custom SMTP gives you domain-level sender control and uses your own mailbox credentials.
Layer 2: Reliability checks
- Always run SMTP connection test before the first production invoice send.
- Keep sender name and address consistent — changing these mid-campaign can affect deliverability.
Layer 3: Delivery monitoring
- Investigate bounces and spam placement early to prevent payment delays.
- Update SMTP credentials promptly when email provider passwords change.
Default sending
By default, invoices are sent via the Resend email platform using a Numwisely-managed sender domain. This requires no configuration and works immediately after Invoice Settings are filled in. The from name is your configured business name; the from address is a Numwisely domain address.
Default sending is suitable for most small and medium businesses. Replies from clients go to your configured reply-to address.
Custom SMTP
Custom SMTP lets you send invoices from your own domain and mailbox (for example, billing@yourcompany.com). This gives you full control over the sender identity, improves brand consistency, and can improve deliverability if your domain has good email reputation.
To configure custom SMTP, go to Invoice Settings → Email Sending. Enter your SMTP host, port, username, and password. Most providers use port 465 with SSL or port 587 with STARTTLS.
- Gmail / Google Workspace: host smtp.gmail.com, port 587, use an App Password (not your main Google account password).
- Outlook / Microsoft 365: host smtp.office365.com, port 587.
- Zoho Mail: host smtp.zoho.eu, port 465.
- Any other provider: consult your email provider's SMTP documentation for the exact host and port.
SMTP setup checklist
Follow this checklist when setting up custom SMTP to avoid delivery failures on the first real invoice send.
- Use the exact SMTP host name from your email provider.
- Use an app-specific password if your provider requires two-factor authentication (Gmail, Outlook).
- Click "Test Connection" after saving to confirm the settings work.
- Send a test invoice to your own email address to verify end-to-end delivery.
- Confirm the reply-to address is set to a mailbox you monitor.
Custom sender from name
You can configure a custom "from name" that appears in the client's inbox (for example, "ACME Corp Billing" instead of a generic app name). This name is configured in Invoice Settings and applies to all invoices sent via the platform.
Common delivery issues
If clients are not receiving invoices, check these in order: verify the client email address is correct; check your SMTP test confirms the connection is active; check your email provider's sent folder to confirm the email was dispatched; ask the client to check their spam folder; verify SPF and DKIM records are configured for your sending domain.
If invoices consistently land in spam at client mailboxes, the most effective long-term fix is to configure SPF, DKIM, and DMARC DNS records for your sender domain. Consult your DNS provider or email administrator for this setup.