Varibill is capable of sending the generated, drillable PDF invoices, statement where the accounting system supports it, and other communications to your customers via email.

To do this Varibill makes use of either the Varibill provided SMTP relay service, or you can elect to use your own SMTP relay service.

General data on Varibill's SMTP service

All emails sent via Varibill is:

  1. Sent via an authenticated account. This is done in the form of a username and password.
  2. Sent via TLS, typically on port 587.
  3. Sent via the standard SMTP protocol.

Using the Varibill provided SMTP relay service

This is the default configuration for you when your tenant is first created. Varibill currently makes use of Twilio's SendGrid, which is included in your hosting fee.

Email is generally sent from an email address on your domain e.g., or or any other email address that you choose. To combat spam and in accordance with best practices, SendGrid requires that the domain is verified as an authorised sender.

Varibill will at setup, send you a list of CNAME records that need to be created in DNS for SendGrid to allow relaying of email for your domain.


  1. You do not need to provide any additional configuration information, except for the initial sender authentication.
  2. The cost of sending email is included in your subscription.


  1. Email is not a guaranteed delivery mechanism, and as such, emails via SendGrid is a best effort service. Varibill cannot provide any mail tracking information.

Using your own SMTP relay service

If you wish to make use of your own SMTP relay server, you will need to provide Varibill with the following:

  • The FQDN or IP address of the SMTP relay server.
  • The port number of the SMTP relay server that makes us of TLS, typically port 587.
  • The full username and password for authentication purposes.
  • The correct permissions on the user account to allow relaying and sending permissions, where the username provided is not the same as the sender address.

Once this data has been provided, Varibill will change the configuration to make use of your own SMTP relay server. Please ensure that you have tested the configuration and that it is working as expected.


  1. You are able to exercise control over email delivery, including tracking and tracing.
  2. No need to perform additional sender verification.


  1. Your service provider may charge an additional fee for your SMTP relay service.


Can Varibill provide a static source IP from which all SMTP relays will originate?

No. Varibill is hosted on Microsoft Azure, and the platform itself does not provide a single static IP address for source     traffic. You can send an email to to obtain the current range of IP addresses that traffic might originate from, but the IP address ranges might change without notice.

Does the username for authentication purposes need to be the same as the email address from which email is sent in Varibill?

No. We recommend that you provide us with a separate user dedicated to Varibill for email relaying purposes. Please do ensure that the user has the relevant permissions to send on behalf of the relevant email addresses.

Which SMTP relay services can I use?

You can use any SMTP relay service that is Internet reachable, supports TLS as well as username and password authentication. This includes Office 365, Amazon SES (Simple Email Service) as well as compliant on-premise SMTP servers.