eM Client Fails to Connect to IMAP

On occasion, when setting up a new SmarterMail account in eM Client using IMAP, the connection fails. When checking the IMAP logs, NTLM errors are seen. That means that the workstation configuration is preventing the use of modern NTLM authentication. This is easily fixed by managing the LAN authentication level for your Windows user account.

While that may sound tricky, it's actually pretty simple. Just do the following:
  1. On your computer, type MMC in the search box. This should give you the option to open the MMC Console. (NOTE: You may need administrator privileges to open this utility, so it's best to right-click the icon and select "Run as Administrator".)
  2. One the MMC is open, you may see that it's essentially empty, showing simply Console Root at the top. This is especially true if you've never used the MMC on your computer before.
    If this is the case, you will need to add in a snap-in, which is very easy to do.
  3. Click on the File menu at the top. From the dropdown, select Add/Remove Snap-in...
  4. A modal opens, with a number of Snap-ins to select. You want to add in the Group Policy Object snap-in. So click on that and then click the Add > button to move it to the Selected snap-ins group.
  5. Before this snap-in can be added, you need to assign it to an object, so the Select Group Policy Object modal opens. By default, "Local Computer" is selected, and this is exactly what you want. So just click the Finish button in this modal.
  6. Next, click the OK button. You'll now see a new item listed under Console Root: Local Computer Policy.
  7. Once the snap-in is added, you need to edit a particular Security Option to allow the use of NTLM authentication. So you need to open a few sections within the Local Computer Policy snap-in. Click the carets next to the following:
    Local Computer Policy
    Computer Configuration
    Windows Settings
    Security Settings
    Local Policies

    Security Options
    Your tree view should look like this:
  8. In the policies listed under Security Options, scroll down to, and double click on, Network security: LAN Manager authentication level to open that policy.
  9. On the Local Security Setting tab, click the dropdown box and, from the options, select Send LM & NTLM - use NTLMv2 session security if negotiated.
  10. Click Apply, then the OK button.
  11. Finally, you'll be asked to save this new console configuration. You can simply close the Console by clicking the X in the upper, right corner and you'll be prompted to save the configuration. You can just use the default name it provides, and do not change the save location. However, saving the configuration is NOT necessary to make the changes you've made permanent -- as soon as you hit the OK button in the Local Security Setting modal, the change you made is saved.
That's it! You should be able to re-try adding in an IMAP account to eM Client and it will all work as designed!