The manpage suggests specifying: Domain => AF_INET. This changes how this is handled in the DNS lookup when both IPv6 and IPv4 records exist.

However this needs to be disambiguated in the Net::SMTP call, prior to IO::Socket::INET being called. This may require changing the host wide resolver behavior to prefer INET4 records to AAAA records, or specifying perl module dns lookup to return A records only. Partial answer to investigate why this new behavior. 

           In addition to the key-value pairs accepted by IO::Socket, 
+ "IO::Socket::INET6" provides.

               Domain      Address family               AF_INET | AF_I
+NET6 | AF_UNSPEC (default)

[download]

           If "Domain" is not given, AF_UNSPEC is assumed, that is, bo
+th AF_INET and AF_INET6 will be both considered when resolving DNS  n
+ames. AF_INET6 is prioritary.

[download]
           (Concrete to IPv4 protocol)

              $sock = IO::Socket::INET6->new(PeerAddr => 'www.perl.org
+',
                                            PeerPort => 'http(80)',
                                            Domain => AF_INET ,
                                            Proto    => 'tcp');

[download]

In reply to Re: Net::SMTP assistance by Anonymous Monk
in thread Net::SMTP assistance by FFSparky

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