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A custom mailbox lets Prosyo send campaign emails through your own mail server (SMTP) and read replies back into your Inbox (IMAP). It works with almost any email provider.
Who can connect one#
| Plan | SMTP/IMAP mailbox |
|---|---|
| 7-day trial | 1 included |
| Starter (paid) | Not included. Starter is LinkedIn-only. |
| Multichannel | Uses your email seat (1 mailbox: SMTP/IMAP or Gmail/Outlook), and you can buy more |
| Agency / Team | Uses an email seat (1 per billed seat: SMTP/IMAP or Gmail/Outlook), and you can buy more |
| Enterprise | Uses the plan's email seats (up to 100 mailboxes: SMTP/IMAP or Gmail/Outlook) |
| Penny SDR All-in | Uses the plan's email seat (1 mailbox: SMTP/IMAP or Gmail/Outlook) |
| AppSumo | 1 included, and you can buy more |
Only owners and admins can add a mailbox.
Need more sending mailboxes? Extra SMTP/IMAP seats are available on Multichannel, Agency / Team and AppSumo plans. See add-ons.
What you need#
- The SMTP host and port of your provider
- The IMAP host and port of your provider
- The mailbox username, usually the full email address
- The mailbox password, or an app password if your account uses two-step verification
Connect#
- Go to Settings → Accounts.
- In the Custom SMTP / IMAP card, click Add SMTP/IMAP.
- Fill in the Add SMTP/IMAP mailbox form:
| Field | What to enter | Example |
|---|---|---|
| SMTP host | Outgoing mail server | smtp.yourdomain.com |
| Port | 587 (STARTTLS) or 465 (SSL) | 587 |
| Use SSL/TLS (port 465) | Tick only when you use port 465 | off |
| Username | Mailbox login | [email protected] |
| Password | Mailbox password or app password | •••••••• |
| IMAP host | Incoming mail server | imap.yourdomain.com |
| Port (IMAP) | Almost always 993 | 993 |
| IMAP username | Leave blank to use the SMTP username | |
| IMAP password | Leave blank to use the SMTP password | |
| From email | The address prospects see | [email protected] |
| From name (optional) | The name prospects see | Priya Sharma |
- Click Verify & connect. Prosyo tests both SMTP and IMAP before saving.
- The mailbox appears as Healthy. Your credentials are stored encrypted.
Settings for common providers#
| Provider | SMTP host | SMTP port | IMAP host | IMAP port | Password |
|---|---|---|---|---|---|
| Google Workspace / Gmail | smtp.gmail.com | 587 | imap.gmail.com | 993 | App password (turn on 2-Step Verification first) |
| Microsoft 365 / Outlook | smtp.office365.com | 587 | outlook.office365.com | 993 | Usually not possible. Use the one-click Outlook connection. See below. |
| Zoho Mail | smtp.zoho.com (smtp.zoho.in / smtp.zoho.eu by region) | 587 or 465 | imap.zoho.com (same region) | 993 | App-specific password if 2FA is on. Turn on IMAP access in Zoho settings. |
| GoDaddy (Microsoft 365) | smtp.office365.com | 587 | outlook.office365.com | 993 | Usually not possible. Use the one-click Outlook connection. See below. |
| Hostinger | smtp.hostinger.com | 465 (SSL) | imap.hostinger.com | 993 | Mailbox password |
| Namecheap Private Email | mail.privateemail.com | 465 (SSL) | mail.privateemail.com | 993 | Mailbox password |
| Yahoo Mail | smtp.mail.yahoo.com | 465 (SSL) | imap.mail.yahoo.com | 993 | App password |
| cPanel hosting | mail.yourdomain.com | 465 (SSL) | mail.yourdomain.com | 993 | Mailbox password |
Provider settings change from time to time. If a value doesn't work, check your provider's help page for "SMTP settings".
Google Workspace / Gmail app password#
- Turn on 2-Step Verification in your Google Account.
- Open https://myaccount.google.com/apppasswords.
- Create an app password named Prosyo and copy the 16-character code.
- Paste it in both the SMTP and IMAP password fields (or only in SMTP, and leave IMAP blank).
If App passwords doesn't appear, your Google Workspace admin has turned it off. Ask them to allow it, or use the one-click Gmail / Google Workspace connection instead.
Microsoft 365 / Outlook#
Prosyo's custom mailbox signs in with a password, and Microsoft no longer allows password sign-in for IMAP on most Microsoft 365 and Outlook.com mailboxes. Use the one-click Outlook / Microsoft 365 connection instead.
Try the settings above only if your Microsoft 365 admin confirms that password sign-in (Authenticated SMTP and IMAP) is still allowed for your mailbox. The admin also checks that both are turned on for it:
- Open the Microsoft 365 admin center → Users → Active users.
- Select your user → Mail tab → Manage email apps.
- Tick Authenticated SMTP and IMAP, then save.
- Wait up to an hour, then connect again in Prosyo.
Before you send: protect your domain#
For good deliverability, make sure your sending domain has:
- SPF, which lists the servers allowed to send for your domain
- DKIM, which signs your messages
- DMARC, which tells receivers what to do with unsigned mail
Your email provider's admin panel shows the exact records to add at your DNS host.
Many teams send outreach from a secondary domain (for example getacme.com instead of acme.com) so their main domain's reputation stays safe. Warm up any new mailbox: start near 25 emails per day and increase slowly.
Custom SMTP/IMAP or Gmail/Outlook?#
| Custom SMTP/IMAP | Gmail / Outlook one-click | |
|---|---|---|
| Works with | Any provider | Google and Microsoft accounts |
| Setup | Host, port and password | Sign in with Google or Microsoft |
| Replies in Inbox | Yes, via IMAP | Yes |
| Plans | Trial, Multichannel, Agency / Team, Enterprise, Penny SDR All-in, AppSumo | Multichannel, Agency / Team, Enterprise, Penny SDR All-in, or an extra LinkedIn/email seat |
| Seat it uses | An email seat or an SMTP/IMAP seat | An email seat or an extra LinkedIn/email seat |
On plans with email seats, each seat holds one mailbox, SMTP/IMAP or Gmail/Outlook, whichever you connect.
Common errors#
| Message or symptom | Fix |
|---|---|
| "Could not connect to the SMTP server" or "Could not connect to the IMAP server" | Check the host, port, username and password. With 2FA, use an app password. On Microsoft 365, see above. |
| Connection timed out | Check the host and port. Try 465 with Use SSL/TLS ticked, or 587 with it unticked. |
| SMTP works, IMAP fails | Turn on IMAP in your mail provider's settings, and check the IMAP host and port 993. |
| Emails send but no replies in Inbox | IMAP is failing. Open Settings → Accounts, click Test connection, then Sync now. |
| You changed the mailbox password | SMTP/IMAP mailboxes have no Reconnect button. An owner or admin disconnects the mailbox and adds it again with the new password. Then pick it under Email accounts on each campaign's Sending & safety tab, and click Review & resume if the campaign paused. |
| No Add SMTP/IMAP button, and the card says Not on Starter | You're on paid Starter, which is LinkedIn-only. Upgrade to Multichannel or Agency / Team. |
| No Add SMTP/IMAP button on Multichannel or Agency / Team | Your email seats are all in use (a Gmail/Outlook mailbox uses one too). Disconnect one, or add an extra SMTP/IMAP seat on Settings → Billing. Also check you're an owner or admin. |
Transactional emails from Prosyo itself, such as sign-in links and receipts, never use your mailbox.
