Feat/support helo customization

README.md

@@ -63,6 +63,19 @@ export POP_SMTP_USERNAME=pop@charm.sh
 export POP_SMTP_PASSWORD=hunter2
 ```
 
+#### Custom HELO
+
+> **Note**:
+> [Some SMTP relays](https://support.google.com/a/answer/2956491?hl=en&fl=1&sjid=11501593087205020993-NA) does not support `localhost` in the HELO CMD (which is the default pop behavior).
+
+To configure HELO value, you can set the following environment variables.
+
+```
+export POP_SMTP_HELO=charm.sh
+```
+
+Or via the cli `pop -c charm.sh`|`pop --smtp.helo charm.sh`
+
 ### Environment
 
 To avoid typing your `From: ` email address, you can also set the `POP_FROM`

email.go

@@ -71,6 +71,7 @@ func sendSMTPEmail(to, cc, bcc []string, from, subject, body string, attachments
 	server.Password = smtpPassword
 	server.Host = smtpHost
 	server.Port = smtpPort
+	server.Helo = smtpHelo
 
 	// Set defaults for gmail.
 	if strings.HasSuffix(server.Username, gmailSuffix) {

main.go

@@ -45,6 +45,9 @@ const PopSMTPPassword = "POP_SMTP_PASSWORD" //nolint:gosec
 // PopSMTPEncryption is the encryption type for the SMTP server if the user is using the SMTP delivery method.
 const PopSMTPEncryption = "POP_SMTP_ENCRYPTION" //nolint:gosec
 
+// PopSMTPHelo is the HELO sent to the SMTP server if the user is using the SMTP delivery method.
+const PopSMTPHelo = "POP_SMTP_HELO"
+
 // PopSMTPInsecureSkipVerify is whether or not to skip TLS verification for the
 // SMTP server if the user is using the SMTP delivery method.
 const PopSMTPInsecureSkipVerify = "POP_SMTP_INSECURE_SKIP_VERIFY"
@@ -67,6 +70,7 @@ var (
 	smtpEncryption         string
 	smtpInsecureSkipVerify bool
 	resendAPIKey           string
+	smtpHelo               string
 )
 
 var rootCmd = &cobra.Command{
@@ -226,6 +230,8 @@ func init() {
 	rootCmd.Flags().BoolVarP(&smtpInsecureSkipVerify, "smtp.insecure", "i", envInsecureSkipVerify, "Skip TLS verification with SMTP server"+commentStyle.Render("($"+PopSMTPInsecureSkipVerify+")"))
 	envResendAPIKey := os.Getenv(ResendAPIKey)
 	rootCmd.Flags().StringVarP(&resendAPIKey, "resend.key", "r", envResendAPIKey, "API key for the Resend.com"+commentStyle.Render("($"+ResendAPIKey+")"))
+	envSMTPHelo := os.Getenv(PopSMTPHelo)
+	rootCmd.Flags().StringVarP(&smtpHelo, "smtp.helo", "c", envSMTPHelo, "Helo sent to the SMTP server"+commentStyle.Render("($"+PopSMTPHelo+")"))
 
 	rootCmd.CompletionOptions.HiddenDefaultCmd = true