Correct, these are time offsets, not time zones. Although, absolute times are exactly what they are for and the reason why e-mail headers use this format. Whene

Correct, these are time offsets, not time zones. Although, absolute times are exactly what they are for and the reason why e-mail headers use this format. Whenever referring to offsets ("+1 day") or reoccurring events such as in a calendar app ("every 4/1 at midnight"), a real timezone is needed. I've seen plenty of code introduce DST related bugs by taking the current timezone offset and using it to do date/time calculation throughout the life of the application.