1. Technical Errors: Problems with the email service provider's system can cause delays or failures in email delivery. 2. Incorrect Scheduling: Human error in setting up the campaign schedule can lead to emails being sent at the wrong time. 3. Time Zone Confusion: Sending emails without accounting for the recipient's time zone can result in emails arriving at inconvenient times. 4. Server Delays: Overloaded or slow servers can delay the sending process.