accuMail uses NHSmail inboxes. Therefore, to make sure emails sent via accuMail are secure, emails can only be sent to email addresses with domains which meet NHSD's secure email standard. Read more about what this means in practice here.
You can spot email addresses which meet NHSD's secure email standard by their endings. They will end in:
Nhs.uk domains accredited to the DCB1596 secure email standard*
There are also a selection of email domains which have gone through NHSD's process to meet their standard; a list of those domains can be found here.
*We've made a recent change which means you can send an email to any nhs.uk email address even if it's not on NHSD's list of accredited domains.
Any emails sent to this type of email address via accuMail can't be guaranteed as secure, as detailed in this help article. accuMail will warn you whenever you're sending to this type of domain. The warning will look similar to the screenshot below.