Many factors like Sequence schedule working hours, timezones, excluding weekends from schedules, safety settings, mailbox sync issues delays emails from getting delivered to the prospect.
During initial days, before you turn on a sequence
Check the schedule you've set for the sequence for active days, working hours and timezone.
Then, verify if you've exceeded the daily sending limits from Outbox - Sent. If you feel you've sent max. no of email that day(in last 24 hours) and still want to start the sequence on same day, increase the daily sending limits from Settings - Safety settings accordingly.
If you're planning to send a mail on weekend, check if that weekend is added with time slots in schedule.
After adding prospects and turning on the sequence,
If the 1st step is an auto email on Day #1, you can see Email scheduled today in sequence - Prospects tab.
Note - Auto emails with no specific time from sequence step will take 5 minutes to get delivered to the prospect(if schedule working hours are still active).
2. Now, Check your outbox-scheduled tab and outbox-sent tab to see if the emails are getting sent as per your added sequence schedule and working hours.
3. If you wish to send immediately, click on scheduled email and send. Your email will be delivered in less that 5 minutes (only if the current time falls under scheduled time).
4. If your email is still not delivered, check the mailbox syncing time from User settings - Mailbox. Make sure that your mailbox is still connected and sync time is less than 5 mins after email sent from outbox.
5. If you don't find your email either in Scheduled or Sent, check Failed section from Outbox.
Tip - Mouse hover on Failed X mins ago to know the reason for email getting failed.
Note - For manual emails, On clicking Send & complete in task execution window, the email will be scheduled as per the sequence timezone. It will not be delivered immediately.
If you're still facing any other issues while sending emails, please contact support.