From the app by default you can't do it.
However, you can email the user or you can use the support tickets extension to open a support ticket from backend for a particular customer, case in which he'll receive your message.
@twisted1919, I'm not saying for support tickets or mass mail. Just a simple notification message as for example Facebook. Where user don't have to reply or anything, only admin can add or send notification to the user account.
@twisted1919, Thanks this what we were looking for. Kindly look for Opening Stats issue as well, as they are not working properly unless the image get loads. Because other ESPs such as SendGrid, MailChimp don't have these issues.
@twisted1919, Thanks for prompt reply. This is was I'm trying to say, in SendGrid it's working perfectly fine. I'll give you a direct example:
We sent one campaign today from MailWizz through SendGrid server to 4 subscribers and guess what. We "0" Open Stats in MailWizz but SendGrid showing 2 Opens.