Recently I’d been having problems sending mail from one of the mail accounts on my iPhone. No error message. The mail just wasn’t being sent. Re-booting the iPhone appeared to sometimes fix the problem, but I couldn’t put my finger on exactly what the issue was until I noticed when it was happening.
If you want your visitors to be able to send you an email from your site there are several options including mailto, sendmail or Postfix. There are also numerous sites offering contact forms for free. For a while I was using the excellent swiftmailer which performed perfectly on both my local and remote servers for a while, but subsequently ceased working on my remote server (presumably because of some configuration change by my hosting provider which I never did get to the bottom of).