SMTP connection timing out - ruby-on-rails

Question

I'm pulling my hair out trying to debug an 'execution expired' error while sending email through Rails' ActionMailer, and having no luck. I don't think that it's a Rails problem as the connection also times out when executing telnet smtp.gmail.com 587 from the terminal as well.
The output when executing the telnet command is:
Trying 2607:f8b0:400d:c07::6c...
telnet: connect to address 2607:f8b0:400d:c07::6c: Operation timed out
Trying 74.125.192.108...
Connected to gmail-smtp-msa.l.google.com.
Escape character is '^]'.
220 smtp.gmail.com ESMTP z32sm7598799qtz.0 - gsmtp
My settings are in config/development.rb as follows:
config.action_mailer.raise_delivery_errors = true
config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {
:address => "smtp.gmail.com",
:port => 587,
:domain => "gmail.com",
:user_name => ENV['GMAIL_USERNAME'],
:password => ENV['GMAIL_PASSWORD'],
:authentication => "plain",
:enable_starttls_auto => true
}
The stack trace is as follows:
Completed 500 Internal Server Error in 30095ms (ActiveRecord: 1.0ms)
Net::OpenTimeout - execution expired:
/Users/yawn/.rbenv/versions/2.1.2/lib/ruby/2.1.0/timeout.rb:114:in `timeout'
/Users/yawn/.rbenv/versions/2.1.2/lib/ruby/2.1.0/net/smtp.rb:550:in `do_start'
/Users/yawn/.rbenv/versions/2.1.2/lib/ruby/2.1.0/net/smtp.rb:520:in `start'
mail (2.6.4) lib/mail/network/delivery_methods/smtp.rb:113:in `deliver!'
mail (2.6.4) lib/mail/message.rb:2149:in `do_delivery'
mail (2.6.4) lib/mail/message.rb:237:in `block in deliver'
...
/Users/yawn/.rbenv/versions/2.1.2/lib/ruby/2.1.0/webrick/server.rb:295:in `block in start_thread'
I have also tried turning on "Allow access for less secure apps" in Gmail, and have tried my personal gmail address as well as a custom domain Google Apps domain. I initially tried it with only the custom domain Google Apps address and thought that maybe Namecheap blocks SMTP connections the same way that I've read that Digital Ocean does, but the problem persisting with a simple #gmail address seems to rule that out.
When I was going down that path, I also tried adding:
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
to /etc/sysctl.conf, but to no avail.
My thinking is now that maybe it's just my ISP blocking SMTP connections and if I were to deploy this to production that maybe it would just work? But I really don't know.
Thanks in advance.