Follow this guide to send mailbox traffic through your own provider: add an SMTP profile, confirm the connection, then assign that profile to native mailboxes. The mailbox address stays the From address.

Overview

This manual explains how to route outbound mail through an external SMTP gateway in two stages:

  1. Add an SMTP profile.

  2. Assign that profile to one or more native mailboxes.

Prerequisites

Before you begin, ensure:

  • You have the SMTP host, port, username, and password (or app password, SMTP key, or API key) from your provider.

  • You already have the native mailboxes you want to send from (for example, sales@example.com).

 

Key Concepts

SMTP profile:  Saved profile credentials (host, port, TLS, username, and password) used to send mail.

Native mailbox:  A mailbox created at Mails.Now, on one of your domains. 

External mailbox:  A mailbox created from an SMTP username that is an email address. No need to assign an external SMTP profile for these mailboxes.

Relay only:  The profile is used for sending. Assigned native mailboxes keep MailAPI IMAP. By using MailAPI IMAP, you can receive all incoming emails on the Mails.now platform for that domain.

Default SMTP profile:  The profile used automatically for native mailboxes that have no SMTP profile assigned. An explicitly assigned profile takes priority.


Configuration / Setup

1) Add an SMTP Profile (Required)

Use this step to store the gateway your mail will leave through.

Open Settings → SMTP/IMAP and choose Add SMTP profile.

Step-by-Step Instructions

  1. Open Settings page. Choose SMTP/IMAP.

  2. Click Add SMTP profile.

  3. Click on your intended SMTP provider card.

  4. Enter Host, Port, and TLS to match the provider.

  5. Enter Username and Password.

  6. Check 'Set up IMAP also' only if you want to assign new IMAP config for assigned mailboxes.

  7. Choose Test connection.

  8. Save the form.

2) Add Gmail SMTP profile

  1. Open Add SMTP profile.

  2. Select Gmail.

  3. Confirm 2FA is enabled on the Google account and enter the app password.

  4. Enter Gmail Address.

  5. Choose Test connection.

  6. Save the form.


Important note: Gmail profiles are send-only. After Save, you can see a mailbox is created for that Gmail address. *IMAP is not stored. 

3) Add Microsoft 365 profile

  1. Open Add SMTP profile.

  2. Select Microsoft 365.

  3. Choose Connect Microsoft 365 and complete the Microsoft sign-in, or choose Connect with SMTP instead and save host, port, username, and password.


Some credential rules by provider:

  • Amazon SES - SES SMTP username and generated SES SMTP password. Not the AWS console login.

  • SendGrid - username apikey, and the API key as the password.

  • Postmark - Server Token as both username and password.

  • Brevo - Brevo login as username and the SMTP key as the password.

  • Mailgun, MailerSend, Emailit - the SMTP username and password from that provider.

*These providers start as relay only.

Form: Add SMTP profile

Choose your email provider to get started.

  • Custom SMTP — any SMTP server. You enter the host.

  • Gmail — personal Gmail. Host and port are fixed.

  • Microsoft 365 — Outlook and Office 365. OAuth is the recommended path. SMTP credentials are the alternate path.

  • Amazon SES, Mailgun, SendGrid, Postmark, MailerSend, Brevo, Emailit — host, port, and TLS are prefilled. Confirm the host matches the region or account your provider gave you.

Required fields (Custom SMTP and provider SMTP)

Host  Provider SMTP hostname: (for example, smtp.example.com). Required except on Gmail, where it is fixed.


Port  Provider SMTP port: Presets use 587. Required except on Gmail, where it is fixed.


TLS  Enable for STARTTLS on port 587. Match the provider’s requirement.


Username: Provider SMTP username. Use an email address, or only letters, numbers, hyphens, underscores, and dots.


Password: Provider SMTP password, app password, SMTP key, or API key. This is not your Mails.Now account password.


Optional fields

Set up IMAP also: Fills IMAP host, port, TLS, username, and password on the profile.

Copy SMTP credentials: It copies the SMTP username and password into the IMAP fields. 


Gmail fields

Gmail Address:  The Gmail address (for example, user@gmail.com).

App Password:  A Gmail app password. 2FA must be enabled. This is not the regular Gmail password.

Host and port are read-only: smtp.gmail.com, port 587.


Microsoft 365 fields

Connect Microsoft 365:  Recommended. Sign in with Microsoft. No app password is required.

Connect with SMTP instead:  Uses the SMTP form. Preset host is smtp.office365.com, port 587, TLS on, relay only by default.

Use Test connection before Save. A successful test is shown as “Yay, your test connection was successful!”


2) Assign the SMTP profile to Mailboxes (Required)

Use this step to let native mailboxes use the SMTP profile you created.

Open Mailboxes, select one or more native mailboxes, then choose Bulk actions → Assign SMTP Relay.

Step-by-Step Instructions

  1. Open Mailboxes.

  2. Select the native mailboxes that should send through this gateway.

  3. Open Bulk actions and choose Assign SMTP Relay.

  4. Select the SMTP profile.

  5. Save.

  6. Confirm the SMTP Profile column on those rows.


Form: Assign SMTP Relay

SMTP relay profile:  Select the profile. *The list shows active, non-MailAPI profiles that have a username and either a host plus password, or a connected Google or Microsoft OAuth profile.

Save:  Save applies that profile to every selected native mailbox.

Important note: If the list says “No assignable SMTP profiles yet,” add the profile in Settings → SMTP/IMAP first.


Default SMTP Profile: Use a default instead of per-mailbox assignment (Optional)

  1. On Settings → SMTP/IMAP, in External SMTP profiles, click 'Set as Default' on one profile.

  2. Native mailboxes with no assigned SMTP profile then use that default when mail is sent.

  3. An assigned profile still overrides the default.

The first external profile saved after a passing connection test becomes the default when the account has no external default yet.


Upload Bulk SMTP

  1. On SMTP/IMAP, choose Upload Bulk SMTP.

  2. Download the sample CSV and import it.

Required columns: name, smtp_host, smtp_port, smtp_encryption, smtp_username, smtp_password.

IMAP columns are optional. If any IMAP column is filled, all IMAP columns for that row are required. IMAP columns are ignored for smtp.gmail.com.

*Profile names in the file must be unique and must not already exist.


Examples / Use Cases

Example 1: Company mailboxes through one gateway

  • Profile: Amazon SES, relay only, host email-smtp.us-east-1.amazonaws.com, port 587, TLS on.

  • Assign that profile to billing@example.com and support@example.com.

  • Outbound mail is submitted and sent through to Amazon SES for billing@example.com and support@example.com. Each message still uses that mailbox as the From address. IMAP stays on MailAPI.


Example 2: Personal Gmail as the gateway

  • Profile: Gmail, user@gmail.com, app password, host smtp.gmail.com, port 587.

  • Assign that profile to sales@example.com when that native mailbox should send through Gmail.

Example 3: One default for unassigned mailboxes

  • Set the SendGrid SMTP profile as Default.

  • Mailboxes with no SMTP Profile assigned, will use the default profile ie., SendGrid. *Mailboxes you assign to SES will still be using Amazon SES.


Troubleshooting

Issue: Test connection failed

  • Confirm host, port, and TLS with the provider. Presets use port 587 with TLS.

  • Use the SMTP password, app password, SMTP key, or API key. Do not use the provider’s web login unless the provider says that value is the SMTP username.

  • For Gmail, confirm 2FA is on and the value is an app password.


Issue: Username is rejected

  • Use an email address, or only letters, numbers, hyphens, underscores, and dots.

  • If the message is “A mailbox with this email address already exists,” choose a username that is not already a mailbox on this account, or use a non-email SMTP username such as apikey.


Issue: Profile does not appear in Assign SMTP Relay

  • The profile must be active and must not be the MailAPI profile.

  • It needs a username, plus a host and password, or a connected Google or Microsoft OAuth profile.


Issue: Assignment reported that no native mailboxes were updated

  • Select mailboxes created on your domains.

  • External mailboxes cannot take a relay assignment. They already belong to the SMTP profile that created them.


Issue: Sent mail did not use the gateway you expected

  • Check the mailbox SMTP Profile column. An assigned profile overrides the default.

  • If the column is empty, sending uses the Default SMTP profile, or MailAPI when no external default exists.


FAQs

Does assigning a relay change the From address?

No. The From address stays the mailbox address.

Does assigning a relay change IMAP?

No. Native mailboxes keep MailAPI IMAP. IMAP saved on the profile is not applied to those mailboxes.

Can one SMTP profile be assigned to many mailboxes?

Yes. Select every native mailbox that should share the SMTP profile, then assign the same profile once.

What is the Default SMTP profile?

It is the profile used for native mailboxes that have no SMTP profile assigned yet. Only one SMTP profile is the default at any time. Setting a new default replaces the previous one.

Why did saving a profile create another mailbox?

When the SMTP username is an email address that is not already a mailbox, the platform creates a companion external mailbox for that address and attaches this profile to it. That companion is not a substitute for assigning the profile to your domain mailboxes.


Best Practices / Tips

  • Run Test connection and confirm a pass before you assign the profile.

  • Assign the profiles on the mailboxes that must use a specific provider. Use Default only for mailboxes that should share one fallback.

  • Use one profile per provider account so a credential change has a single place to update.

  • Reassign mailboxes before you delete a profile. Deletion is blocked while mailboxes still use it.


Warnings / Notes

Warning: A Gmail app password requires 2FA. The regular Gmail password will not authenticate.

Warning: Provider presets are relay only by default. Disabling Relay only requires a complete IMAP host, port, username, and password. Partial IMAP data is rejected.

Warning: Assignment updates native mailboxes only. External mailboxes in the selection are skipped.

Warning: The first external profile that passes Test connection becomes the default when no external default exists. Later profiles do not replace it unless you choose Set as Default.


Conclusion

Add the SMTP profile with the provider’s host and credentials, confirm Test connection, then assign that profile to the native mailboxes that should send through it.