FR: have it as an SMTP option.
Great deliverability and cheaper than sendgrind and friends.
It seems they don't offer SMTP relay as per https://www.mailerlite.com/help/does-mailerlite-offer-smtp-simple-mail-transfer-protocol . Their partner company mailersend has it - https://www.mailersend.com/help/smtp-relay . If you can, please try using mailersend with Cloudron's External SMTP Server option - https://docs.cloudron.io/email/#relay-outbound-mails . If that works well, I can add it to the dropdown (the dropdown is really just a UI template to prefill things).