Email module HELO command when sending email

We are currently building a application for a customer and using the module "E-mail module with templates" in this project. The email module should be going to work with the own SMTP server of the customer. During testing, we found out that this will not going work, because the customer's SMTP server demands a FQDN in the HELO command when sending email. Currently, the email module sends "HELO Server01" in which Server01 is the (on-premise) server the application is running on. Although I doubt that a sending email client always have to have a FQDN (an outlook client doesn't have a FQDN either), does anyone has a smart tip how the email module's HELO command can be influenced?
1 answers

In the class you might be able to set the mail.smtp.localhost property that you need,