# Troubleshooting IMAP configuration

Source: https://developer.nylas.com/docs/provider-guides/imap/troubleshooting/

This page describes common issues you might encounter when using IMAP accounts with Nylas and how to troubleshoot them.

## Passwords and character encoding

Nylas currently can't authenticate an IMAP account if its password contains characters that are not in the [ASCII character encoding](https://en.wikipedia.org/wiki/ASCII). If you encounter an error during authentication, check if the account's password contains characters outside the ASCII range. If it does, advise the user to update their password.

## Troubleshoot `UIDVALIDITY` errors

When syncing messages with a provider, Nylas requires a persistent unique identifier across sessions. This ensures data remains consistent and up-to-date. When Nylas syncs an IMAP account, it uses two important identifiers to link the locally cached messages with those on the IMAP server:

- [`UID`](https://www.rfc-editor.org/rfc/rfc3501#section-2.3.1.1)
- [`UIDVALIDITY`](https://www.rfc-editor.org/rfc/rfc3501#section-2.3.1.1)

If any `UID`s changed between sessions, the provider uses the `UIDVALIDITY` value to signal that you need to clear your cache and look for the new `UID`s.

> **Warn:** 
> **For misconfigured providers, the `UIDVALIDITY` value might change with every session**. Nylas uses several concurrent sessions to monitor IMAP accounts, and if each one has a different set of `UID`s, maintaining data consistency is impossible. In these cases, Nylas stops syncing and presents a ["Stopped due to too many `UIDVALIDITY` resyncs" error](#error-stopped-due-to-too-many-uidvalidity-resyncs).

### Error: Stopped due to too many `UIDVALIDITY` resyncs

> Resynced more than MAX_UIDINVALID_RESYNCS in a row. Stopping sync.

If an account is in a Stopped state and the mailsync logs return the error above, this indicates that Nylas stopped syncing the account because of inconsistent `UIDVALIDITY` values between sessions. Because Nylas syncs across multiple sessions for an account, Nylas can't link IMAP `UID`s if the `UIDVALIDITY` value changes constantly.

> **Error:** 
> **Servers with inconsistent `UIDVALIDITY` are not supported until they adhere to the standards set forth in [**the RFC standard document**](https://www.rfc-editor.org/rfc/rfc3501#section-2.3.1.1)**. Nylas cannot work around the issue.

### `UIDVALIDITY` and empty folders

In some cases, the `UIDVALIDITY` error is triggered on folders that contain no messages (and so have no `UIDVALIDITY` values). If this happens, the user can either...

- Delete any empty folders.
- Add at least one message to every empty folder and allow their account to resync.

### `UIDVALIDITY` and Amazon WorkMail

If you connected an Amazon WorkMail account to Nylas using IMAP, your account might be in a Stopped state and you might find the following error in the mailsync logs.

> Resynced more than MAX_UIDINVALID_RESYNCS in a row. Stopping sync.

The error message indicates that the email server doesn't maintain consistent `UIDVALIDITY` values, and is therefore incompatible with Nylas.

You might be able to solve this issue by authenticating your Amazon WorkMail account using [Microsoft Exchange's advanced login settings](/docs/provider-guides/exchange-on-prem/#log-in-using-advanced-settings) and specifying one of the following server addresses, depending on your account region:

- `mobile.mail.eu-west-1.awsapps.com`
- `mobile.mail.us-west-2.awsapps.com`
- `mobile.mail.us-east-1.awsapps.com`