MailClark adds an 👁️ reaction to the ‘Email sent’ notifications when at least one recipient has read the email.
For email groups, there’s also a specific
@mailclark track command.
To track reads, MailClark—like most email service providers—uses a tiny, transparent image hidden in the email’s body. Since some mailers block images by default, MailClark is unable to track 100% of reads.