Ketika SMTP error timeout. Jika di Ruby/Rails seperti ini :
Net::OpenTimeout (execution expired): net/smtp.rb:539:in `initialize`
Penyebabnya karena secara default kebanyakan ISP port 25 / 587 diblokir.
Solusinya diganti pakai port 2525
Referensi:
- https://documentation.mailgun.com/en/latest/faqs.html#i-am-getting-timeouts-when-connecting-via-smtp-why