Emails in sent box but recipients not receiving them

Hope someone can help.
My sent emails appear in the sent box nut are not being received. I checked this with a number of people I had sent emails to over the last couple of days after I hadn’t received a reply.

The obvious: Receivers have checked their spam/junk folders?

Any errors in the Menu > OPERATIONS tabs?
Different/same domains for the sent emails?

Hi, Thank you for replying to my query. Yes I did ask the receivers to check their spam/junk folders. There are no errors in the menu - operations tabs, and the emails were to different domains. I have two email addresses and even tried sending one to the other but it was not received?. Hope you can help.

If the messages appear in your Sent folder, then they have most likely been successfully uploaded to the server. So the issue is not with eM Client.

Can you add another email account, say a free account from a provider like Gmail, and try sending from that account.

If they arrive at their destination then it may be that your original email provider is not sending them once they arrive at the server.