Steps to reproduce the issue

• Registration form loads normally
• Enter the usual details for a new user being registered
• Enter email address (1st time), click/tab to "confirm email" field, the form shows an error as below.

Expected result

Successful submission with the usual "You will need to validate your email by clicking the link...." message.

Actual result

Does not submit registration. Shows error (beneath the first of the two email fields) "Connection failed with status: OK".
This occurs with using Joomla core registration form and also in a third party registration component, Ultimate User Lite edition v 1.8.4 - https://extensions.joomla.org/extensions/extension/access-a-security/site-access/ultimate-user-lite/ as listed on JED.

System information (as much as possible)

Joomla 3.8.1
PHP 7.0.16

Additional comments

Don't recall this happening prior to 3.8.x. I don't know if it's just my system.

I can create users as a Super User in the Administrator.

Also posted on Joomla forum: https://forum.joomla.org/viewtopic.php?f=706&t=955750

Try both registration forms here: https://www.murraywebs.net/dev2/
(links: "Ultimate User Reg" and "Core Joomla Reg") or click "Register" on the login form at foot of the page.