“I never received that email.”
This is not what you want to hear from your client. You sent through information detailing their latest proposed project from budgets to schedule. They have to have received it.
“Are you sure?” you ask.
“Yep. Never got it.”
You frantically scroll through your sent messages. There it is, the message you sent. It sent.
“I sent it. I sent it twice. It’s your problem and not mine.” You can’t actually say this, but you think it.
“Let me send it to you again. My apologies.”
You send it again. They still don’t get it. At least not in their inbox.
What’s happened? Your email ended up in their spam folder. Something from your email address for some reason was labeled as spam. There’s no way to control the other side, the receiving spam filters. You can title your email *Not SPAM – MUST READ!* as much as you want, but you can’t control the other side.
A spammer could have gotten control of accounts on your SMTP server and started sending out spam emails without your knowledge. Even if your IT company catches it and stops a spammer from hijacking your servers, which they can, your email address still may be marked as spammer address by some other company servers.
What you have to do, because there’s also nothing your IT company can do about it, is ask the recipient to mark you email address as not spam.
As the filters learn and update, little by little, you’ll make your way out from being marked by their filters as a spammer.
There’s nothing you could have done differently, and there’s nothing your IT company can do to change things. This can and may happen. Be patient and you’ll get back into the inboxes of your clients, but let them know to double check their spam folders for any emails from you.