In Dublin, IST means Irish Standard Time: UTC+1, the clock Ireland keeps in summer. The tz database notes that Irish law since 1971 treats the winter clock, GMT, as a negative daylight saving from that standard. India Standard Time is UTC+5:30 all year. A scheduling screen that just says IST can mean either, and a campaign meant for 09:00 in Dublin can leave at 09:00 in India, four and a half hours early.
Ireland follows the EU change dates, the last Sunday in March and the last Sunday in October. So Dublin is five and a half hours behind India in winter and four and a half in summer. Set every Dublin schedule with the zone name Europe/Dublin, never the abbreviation.
Dublin landlines start 01, written +353 1 from abroad; mobiles start 08 and drop the 0 after +353. InfiQ's own support team works India time, in English and Hindi.