SQLite date format change

I am trying to query apple mail database. However, I can't figure out what time format apple mail sqlite database is using. ZDATE field type is TIMESTAMP. However, it displays date like 278433563.174197. I tried to convert this with the following query. However, it shows completely unexpected result.

select date(ZDATE) from ZABCDLASTEMAILDATE;

The above returns 757612-8421479-06

select datetime(278433563.174197, 'unixepoch');

The above returns 1978-10-28 14:39:23 . This cannot be the actual date.

select strftime('%d-%m-%Y',datetime(278433563.174197, 'unixepoch'));

The above returns 28-10-1978

Can anyone please tell how to get the actual result from that timestamp field of apple mail?