Instead of using AUTH LOGIN, it's using AUTH PLAIN The SMTP server tells it OK to use AUTH PLAIN 
Net::SMTP=GLOB(0xa6fd440)<<< 250-AUTH PLAIN LOGIN
Net::SMTP=GLOB(0xa6fd440)>>> AUTH PLAIN

[download]
PLAIN is listed before LOGIN.

2. The Base64 string contains the username twice, then the password, which is wrong. Is this a bug in Net::SMTP, or a problem with my mail server, or something else?

Maybe, check for updates 

perl -MDevel::Modlist -MNet::SMTP -e 1
Carp                   1.10
Config
Errno                   1.1
Exporter               5.63
Exporter::Heavy        5.63
IO                     1.25
IO::Handle             1.28
IO::Socket             1.31
IO::Socket::INET       1.31
IO::Socket::UNIX       1.23
Net::Cmd               2.29
Net::Config            1.11
Net::SMTP              2.31
SelectSaver            1.01
Socket                 1.81
Symbol                 1.06
XSLoader               0.10
utf8                   1.07
vars                   1.01
warnings             1.05_01
warnings::register     1.01

[download]

In reply to Re: Net::SMTP auth login fails - passes in username twice! by Anonymous Monk
in thread Net::SMTP auth login fails - passes in username twice! by m0thr4

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