Instantly is one of the most popular tools for running cold email campaigns, and you can connect your Maildoso mailboxes to it in just a few steps. This guide walks you through the setup and helps you fix the errors people run into most often.
Before you start
Make sure your mailboxes are showing as Active in Maildoso. Newly created mailboxes can take a little time to finish setting up, and they can only be exported once they are active.
Have your Instantly login details handy — you'll connect using your Instantly login email and password, not an API key.
If your Instantly account has two-factor authentication (2FA) turned on, temporarily disable it before connecting, as it can block the connection.
Step 1: Connect your Instantly account
In Maildoso, click your profile picture in the top-right corner and open Settings.
Go to Sequencers, choose Instantly, and click Configure.
Enter your Instantly login email and password, then click Configure to save the connection.
Step 2: Add your mailboxes to Instantly
Open the Email Accounts section.
Click Export Accounts, then Add all Google Accounts to Sequencer.
Choose Instantly and confirm with Add to Sequencer.
Your mailboxes will begin connecting. This usually completes within 24 hours, after which they'll appear in your Instantly workspace ready to send.
"Request failed with status code 422"
This is the most common error people see when importing Maildoso SMTP mailboxes into Instantly. In most cases it does not mean the mailbox is broken or that it wasn't created.
What it usually is. The 422 comes from an IMAP validation check that failed at the moment of import. The mailbox itself is normally created correctly on our side, and an automated process on our end corrects the underlying IMAP issue shortly afterwards. It is also completely normal for only some rows in your file to fail while the rest import fine — that does not mean anything is wrong with those particular mailboxes or domains.
What to do
Open your Email Accounts page and check the addresses that failed. If they show as Active, the mailboxes are fine — the error refers to the import attempt, not to the mailbox itself.
Wait a little while, then export a fresh CSV (Email Accounts → Export all to CSV) and import that new file into Instantly. Exporting again matters — an older file can still carry the details that failed the first time.
What won't help
Adding the failed mailboxes one by one in Instantly. If the IMAP check is failing, manual entry returns an authentication or IMAP connection error too.
Changing the SSL settings on IMAP or SMTP. That is not what causes a 422.
Re-uploading the same unchanged file straight away — give it a little time and export a fresh CSV first.
When to contact us. Get in touch if the same addresses still fail after you've waited and retried with a freshly exported CSV, or if those mailboxes are not showing as Active. Also note that an expired subscription, or having more mailboxes or domains than your plan covers, takes the affected accounts out of the active state — they can't be imported until your plan covers them again.
Other errors while connecting or importing
Other errors during setup almost always come down to one of the following. Check these in order:
Your mailboxes aren't active yet. If any accounts still show as pending or inactive, wait until they're fully Active and then retry the export. Accounts that aren't active can't be imported.
The Instantly credentials need a second look. Re-open Settings → Sequencers → Instantly → Configure and confirm you entered your Instantly login email and password (not an API key), and that 2FA is turned off on that Instantly account.
Your subscription needs attention. If your plan has expired, or you have more mailboxes or domains than your current plan covers, the affected accounts drop out of the active state and won't connect. Renewing or updating your subscription so it covers all of your mailboxes and domains restores them to active, and the import will then go through.
A note on Google Workspace mailboxes
Google Workspace mailboxes connect using the sender credentials we provide for each account, rather than IMAP. When you export your accounts to Instantly, the correct connection details are included automatically, so you don't need to look them up yourself.
Still stuck after checking the steps above? Contact us with the mailboxes that are failing to connect and we'll review your specific case and get them working.