IMAP Connection Error: "Unable to get a response from the IMAP server"

When trying to connect a custom IMAP mailbox using Hosted Auth or Custom Auth, you might run into one of these errors:

“Unable to get a response from the IMAP server ‘’”

“Unable to get a response from the IMAP server. We detected potential hosts that you can try: …”

Error type: provider_connection_failed
HTTP status: 400

In many cases, the email provider confirms that the mailbox itself is valid and working — so what’s going on?

What’s causing this?

This error usually means that Nylas can’t establish a network connection to the IMAP server.

The most common reason is a firewall or IP restriction on the email provider’s side. 

This tends to happen more often with shared hosting providers like SiteGround, Hostinger, GoDaddy, and similar services that limit access from cloud-based IP ranges.

How to fix it

1. Check for IP restrictions with the email provider

Reach out to the email hosting provider and ask:

“Are there any firewall rules or IP restrictions blocking IMAP (993) or SMTP (465/587) connections from cloud infrastructure ?”

They should be able to confirm if anything is being blocked.

2. Whitelist Nylas IP addresses

If there are restrictions in place, ask the provider to allow (whitelist) Nylas IPs.

You can share this documentation with them:

👉 https://developer.nylas.com/docs/dev-guide/platform/static-ips/

These are Nylas’ static IPs, and they need to be allowed for both IMAP and SMTP access.

3. Let Nylas know Once the IPs have been whitelisted:

Contact Nylas support Ask them to enable static IPs on your account

After that, try connecting the mailbox again — it should go through successfully.

Need More Help?

If you're still experiencing issues after following the steps above, contact Nylas Support with the following information:

• Your Application ID
• The IMAP/SMTP host and port you are using
• The error message and request ID (Support ID) from the failed attempt
• Confirmation from your email provider on whether IP whitelisting has been completed

Updated May 05, 2026 16:49