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
- Without your own mail server, numwisely sends for you as “<your business> via numwisely” once your business is verified.
- Custom SMTP gives you domain-level sender control and uses your own mailbox credentials.
Layer 2: Reliability checks
- Your own mail server is used only after its test email went out successfully.
- 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.
Sending through numwisely
Without your own mail server, invoices are sent from a numwisely address with the sender name “<your business> via numwisely”, so the client sees who the invoice is from and that numwisely delivered it. Replies go to your own address.
numwisely sends on your behalf only once your business is verified (Invoice settings → Business → Verify now). Until then, connect your own mail server to send invoices.
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 set it up, go to Invoice settings → Delivery → Email sending. Enter the from address — common providers are filled in for you — then the server, port, username and password. Most providers use port 465 with SSL or port 587 with STARTTLS. Only public mail servers on ports 25, 465, 587 or 2525 can be used.
- 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).
- Select “Save & send test email”: numwisely sends a real test email through your server to your own address. Your server is used for invoices only after this test succeeded.
- Send a test invoice to yourself from the send dialog (“Send a test to me”) to check the whole email.
- Confirm the reply-to address is set to a mailbox you monitor.
If your mail server fails
When your own server rejects an invoice email, the send fails and you see the reason — for example that the login was rejected or the sender address isn’t allowed. Nothing goes out from another address without your consent.
If you prefer the invoice to go out anyway, turn on “Send through numwisely instead” under Invoice settings → Delivery. It is available once your business is verified.
With your own server, the sender name is the one you set under Email sending; recurring invoices can use their own sender name.
A copy is saved to your Sent folder
When you send an invoice through your own SMTP server, numwisely also files a copy in your mailbox's Sent folder, so it appears alongside the rest of your sent mail — exactly like a message you sent yourself. This is automatic and needs no extra setup: it reuses your saved SMTP credentials.
Providers that already save sent mail on their own (such as Gmail and Outlook / Microsoft 365) are left untouched, so you never get duplicate copies. Filing the copy is best-effort — if your mailbox is briefly unreachable it is skipped and the invoice is still delivered to the client. This applies only when you send through your own SMTP; emails sent through numwisely don’t touch your mailbox.
Common delivery issues
If clients are not receiving invoices, check these in order: verify the client email address is correct; check the activity list on the invoice for the send and its from address; send the SMTP test email again; 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.