Hikashop user activation mail not getting sent

-- HikaShop version -- : 3.3.0
-- Joomla version -- : 3.8.5

Hello,

We have a problem when customers are registering on our web shop.
They don't get the activation link and we receive the email with mail body attached and next error:

host outbound.mailspamprotection.com [IP address]
SMTP error from remote mail server after end of data:
550 High probability of spam

We asked web host support about this and they said that everything is set perfectly regarding our e-mail accounts.
They said that we should try and test to find out which character, word or link in our activation mail triggers outbound mail spamprotection.
We weren't able to find out what causes this, we also tried some other solutions like disabling multipart sending but the issue is still the same.
Please help us and If You need we will give You access so You can check the settings out.

Thanks in advance.

Hello,

Hikashop emails are sent using the Joomla mailing system, so that solution will probably be to directly check options of the "Mail Settings" tab via "Joomla->System->Global configuration->Server".

Hello Mohamed,

Thanks for reply, we checked those settings, Mailer was set to PHP mail, we switched to SMTP but still only the problem with hikashop registration mails with activation link get blocked... Any other suggestions?

Hi Nicolas,

I have attached the image of mail-tester result.
I sent the registration mail(both subject and full content) to mail-tester.com using outlook.

It couldn't be sent and tested through our site using registration form as it gets blocked by outbound mail protection and the mail never arrives to receiver....

This is a huge problem for our business as no new user can register.