The higher the TTL (time to live) the longer a hijacked domain needs to stay hijacked before it can reach the masses. Many services use low TTL; for instance, only one minute, for load-balancing purposes. Using high TTL for mail exchanger (MX) records in a DNS adds a delay for hijacking emails. Using email encryption such as PGP (pretty good privacy) will also ensure that attackers can’t steal the information in the emails. Use high TTL (TTL) for MX records to delay the hijackers’ ability to reroute your emails.”]
Source: https://www.darkreading.com/attacks-breaches/thwart-dns-hijackers-5-tips