sender

type IsResolvableOptions struct {
	// FallbackToAddressRecord allows to delivery to 25th port of address resolved by A or AAAA
	// queries if MX records are not present
	// See https://en.wikipedia.org/wiki/MX_record#Fallback_to_the_address_record
	FallbackToAddressRecord bool

	// AllowLocalAddresses means we accept email from domains, which MX records are resolved
	// into local IP addresses according to https://rfc-editor.org/rfc/rfc1918.html (IPv4 addresses) and
	// https://rfc-editor.org/rfc/rfc4193.html (IPv6 addresses).
	// For example, MX for something.example.org are `mx.something.example.org 10`, and
	// A record for mx.something.example.org is 192.168.1.3 - it is unusual case for
	// internet, but common for local networks.
	AllowLocalAddresses bool

	// AllowMxRecordToBeIP allows MX records to contain bare IP addresses, its unsafe, but still used
	AllowMxRecordToBeIP bool

	// DomainsToTrust is whitelist of domains you consider resolvable - for example, this is
	// local domain of your company with MX server having local IP in local network, and
	// on the same time, they are reachable from external network by white IPs.
	// So, IsResolvable should allow senders from this domains to be used for MAIL FROM
	DomainsToTrust []string
}