How to use SMTPUTF8 with Exim

Introduction

If you have clients that are attempting to make use of SMTPUTF8 while your server does not have it enabled, you may see errors similar to the following in the /var/log/exim_mainlog

2021-11-15 12:26:00.383 [3539516] SMTP syntax error in "MAIL FROM: <sender@example.tld> SMTPUTF8

" H=(hostname) [203.0.113.2]:55653 I=[203.0.113.2]:465 SMTPUTF8 used when not advertised

In order to use SMTPUTF8 with Exim, you'll need to enable the following configurations. 

Procedure

1. Log in to WHM as the root user
2. Navigate to "Home / Service Configuration / Exim Configuration Manager"
3. Click on the Advanced Editor tab
4. Find the blue button that says "Add Additional Configuration Setting" and click on it
5. Add the following configurations:

   allow_utf8_domains = true
   
   smtputf8_advertise_hosts = *

6. Scroll to the bottom of the page and click the blue save button

Please review the Exim Documentation for the full information on these configurations:

Exim Documentation - Main Configuration