I'm sending emails out of ESC, but they are not being received.

When an email is sent from ESC, it appears to send without any errors. However, the intended recipient never receives the email.

Cause of Issue:

If no error appears when the email is sent, then it successfully made it through the outgoing mail server. However, with Spam and Junk mail being an ever-increasing problem for the public, many email providers are bumping up their security protocols. This may mean your messages are being blocked by the incoming mail server before they ever reach the recipient's inbox. If those messages do not reach an inbox first, they will not be forwarded to the user's Junk or Spam folder.

Resolution:

• One thing you can do is provide your customers with your outgoing email address (which is the one under the Email tab in System Setup) so that they can add you to their list as a ‘Safe Sender’ and you won’t get blocked. 
• You can also try adjusting the display name for those emails. Many of the bigger email hosts are going crazy with security settings and are blocking things based on their sending name. You can change yours by going to Company → System Setup → Email → Addresses. You’ll want to change the Display Name. If you’re using your company name as the Display Name, try something like “Sales Department” – or visa versa.
• Another issue that could be causing your emails to get blocked is having a Return Address that is different than your actual sending address. Whenever you receive Spam or Junk mail in your inbox, the email address on the message is NEVER the actual email address that sent the message. That would make it too easy for them to track. So many email providers will block messages that show a different Return Address. You can address this in the System Setup → Email → Addresses tab by making the Return Address the same email as the address being used to send the messages (which is listed under the Email tab). This may not be ideal for properly routing reply emails from your customers, but it may be a necessary measure to ensure they are receiving their invoices/quotes.
• There’s really not a lot you can do on your side to get through someone else’s security measures, but you can explain the situation to customers when they contact you. If they call and ask why they haven’t received their invoice or quote, you can let them know to make you a Safe Sender on their end so that they don’t get blocked. The email address you’re using to send the messages is most likely the one to use, but it would be safe to give them both – the one being used to send the email and the Return Address.