Mail Not Reaching Recipients

I’m new to Mainspring as my Apple Mail app puked using Mac OS 10.11.6 (El Capitan).

Why is it that some recipients get my emails while others don’t? This is very frustrating and, at times, catastrophic. Using Mainspring version 1.9.2.

Can anyone please help me with this?

Are all the emails going from the same account, or is the failure related to a specific email account? Do the failed emails appear in your Sent folder, or are they perhaps still in Drafts?

If you can work out any common factor in what you’re doing that might influence the failures, that would really help. Unless you can be specific, it’s really hard for us internet randos to help, unfortunately.

All the email were sent from my account. They appear in the “Sent Messages” folder.

In sending from my iPhone they get my emails, so it’s a Mailspring problem. Need anything else?

Is the email address connected to Mailspring using the iCloud option or as a standard IMAP account? Perhaps try the other option if it’s not working properly?

I assume it was an IMAP account but I just updated connection settings to my iCloud account. We’ll see what happens.