Retry mechanism to send an email from different host

Question

I'm sending an email using nodemailer and in case a send is faild, I wanna use a different host in a retry.

I tried:

let tries = 0;
let maxTries = 2;
  const sendEmail = async () => {
    tries += 1;
    
    if (tries === maxTries) return;

    const transporter = nodemailer.createTransport({
        host: tries === 1 ? host1 : host2,
        port: port,
        secure: false
    });

    // mailOptions object here....

    await transporter.sendMail(mailOptions, (err, info) => {
        if (err) {
            return sendEmail();
          } else {
            console.log('Email Sent Successfuly');
        }
    });
}

It works but it feels a bit cumbersome.

Is there a better way to implement this feature?

This question would probably be a better fit for the [Code Review](https://codereview.stackexchange.com/) site. — Moshe Katz, Mar 20 '22 at 21:52

Scott Sauyet · Accepted Answer · 2022-03-21T00:25:20.797

How about something like this (updated per suggestions from Bergi)?

const sendEmail = async (mailOptions, hosts = [host1, host2]) => {
  if (hosts .length == 0) {
    return Promise .reject ('all hosts failed')
  }
  // configure transporter  
  try { 
    const info = await transporter .sendMail (mailOptions); 
    return 'Email sent successfully'; 
  } catch (err) { 
    return sendEmail (option, hosts .slice (1)) 
  }
}

(Please don't use this original verion, for the reason's Bergi pointed out)

// DO NOT USE
const sendEmail = async (options, hosts = [host1, host2]) => {
  if (hosts .length == 0) {
    return Promise .reject ('all hosts failed')
  }
  // configure transporter
  return new Promise ((resolve, reject) => {
    transporter .sendMail (mailOptions, (err, info) => {
      if (err) {
        return sendEmail (option, hosts .slice (1))
      } else {
        resolve ('Email Sent Successfuly');
      }
    })
  })
}

It could easily be extended to handle something like:

const hosts = [{host: host1, tries: 3}, {host: host2, tries: 1}, {host: host3, tries: 5}]
sendMail (options, hosts)

so that it would try the first host three times, then a second one once, then a third one five times before giving up.

https://nodemailer.com/usage/: "*If callback argument is not set then the method returns a Promise object.*" - so just use `try { const info = await transporter.sendMail(mailOptions); return 'Email sent successfully'; } catch(err) { return sendEmail (option, hosts.slice (1)) }`. This also fixes the broken `return` in your [`Promise` constructor antipattern](https://stackoverflow.com/q/23803743/1048572?What-is-the-promise-construction-antipattern-and-how-to-avoid-it) :-) — Bergi, Mar 20 '22 at 23:43
@Bergi: I guess I should have looked up `nodemailer`. I've never used it. But much worse is getting the Promise wrong like this. (Don't tell all the juniors I ding for this in code review, ok? ;-) ) — Scott Sauyet, Mar 21 '22 at 00:15

Retry mechanism to send an email from different host

1 Answers1