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Fixing email error “435 Unable to authenticate at present” in cPanel, DirectAdmin, Ajenti and other Exim servers

Fixing email error “435 Unable to authenticate at present” in cPanel, DirectAdmin, Ajenti and other Exim servers provides outsourced hosting support to web hosts. As part of our services, we manage the tech support help desk of web hosts, and resolve issues posted by web hosting customers.

Many of our customers use Linux servers that run Exim as their mail server. Exim is usually present in web control panels such as Cpanel, DirectAdmin, Ajenti and more.

A common email error that we see in these servers is 435 Unable to authenticate at present. This is faced by email users when they try to send SMTP authenticated mail through the Exim server either through webmail (eg. Horde) or from an external mail service provider (Eg. Google’s Gmail).

What causes error 435 Unable to authenticate at present?

In short, this error happens when Exim is unable to check if the Username and Password given by the mail user is indeed correct.

It can happen due to:

  • Failure of service that provides authentication (eg. Dovecot)
  • Incorrect mailbox permissions
  • User exceeding mail limits
  • Incorrect SMTP Port settings at the email user’s client
  • Corrupted auth libraries
  • Disk quota issues

Let’s take a look at each of these issues one by one, and see how to fix it.

See how we help web hosting companies

Before we begin – a word of caution

Many server owners troubleshoot issues by trial and error. That is – Do X. Did it fix it? No? Then do Y.

It is not the best way to resolve issues, because:

  • It takes a lot of time to go through all possibilities.
  • A command executed without knowing the full impact of it could result in other services failing.
  • In case something does go wrong, it’s hard to recover from it without knowing what changes the command made.
  • Your server could have custom settings that can conflict with standard commands.

That is why we always recommend our customers to not make changes directly on the server, and instead escalate it to our 24/7 support team.

Our team uses an evidence based approach to solve issues. We look at logs, trace the sequence of events, and then find out exactly where the link is broken. It helps us solve issues faster, and prevent errors.

With that said, let’s now look at the top fixes for this error.


1. Quick fix – Restart POP/IMAP service

In some servers we’ve observed the POP/IMAP service failing to authenticate because of temporary data write issues.

So, a quick fix is to check if the database services are running OK, if the /tmp directory is clear, the disk health is OK, and then restart the POP/IMAP service.

In cPanel servers, this service is DoveCot.


2. Fix mail box permissions

When a login request is sent to POP/IMAP service, the server checks whether the mail directory is in fact accessible. If it is not, the IMAP server gives a fail signal to Exim, and this error will be shown.

So, if this account was recently migrated in, or was un-suspended, or any other recent changes were made, it’ll be a good idea to repair the mailbox permissions.

In cPanel servers, this can be done by:

  1. Login to WHM
  2. Locate the Email section in the left-side panel
  3. Select Repair Mailbox permissions
  4. Click Proceed.
435 Unable to authenticate at present code(435) repair mailbox

Repair mailbox in WHM


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