You can use iOS 12 shortcuts in AltaMail using the device Settings app - Siri & Search - AltaMail (in the lower part of the screen) (Apple help)
You can assign a voice command to the shortcuts using the "+" button beside each shortcut. You can also add shortcuts to your macros in the Shortcuts app.

When you use the left side panel to view a screen such as a Folder Filter, Split screen, Locations etc, most screens support Siri Shortcuts and will show an "Add to Siri" option in the bottom of the action menu (button with the circle and 3 dots icon). When you tap on "Add to Siri" you will be prompted to add a voice command for the shortcut and this will be saved in the device Settings app - Siri - Shortcuts section. You can use the voice command you just created to repeat the action you just did.
When you create a new email you can also use "Add to Siri" in the action menu to create a new email again and then you can edit the message and send it. When you choose "Add to Siri" when sending a template to contacts, the voice shortcut will send that template to the same users again without needing to open AltaMail. For example if you want to tell people you are on your way home or call a meeting by sending a template to a list of contacts. This can also be used in the Shortcuts, eg. tell Siri - "Call a sales meeting"

By default you will see the shortcuts "Enable notification sounds" and "Disable notification sounds". eg. These can be used when you are in a meeting. When you manually disable the notification sounds inside the AltaMail Notification Settings, a new shortcut will be suggested with the time range in hours that you entered. So you could disable sounds for 8 hours.
You could also use the shortcuts app to merge several shortcuts into one. (Apple help)
eg. If you create a custom shortcut in the Shortcuts app called "I am awake", you could add the AltaMail "Enable notification sounds" shortcut to the list as one of the actions. You could also create a "Good night" shortcut that includes the AltaMail "Disable notification sounds" shortcut for 8 hours.
Of course, you can still use the alternate option of setting a schedule to disable notifications and sounds in the Notification Settings. View

You can also send an email from AltaMail using Siri by using the phrase "Send a message using AltaMail", "Send a message to John using AltaMail" or "Send a message to John using AltaMail saying Hi John I will be there soon"
If some additional details are required then Siri will ask for them, such as the recipient or message.
Currently the subject for a new message is predefined in the AltaMail app settings - Email section.
For security reasons, AltaMail will ask for access to send emails when the first email is created with Siri. This can be changed in the app settings - Security section. You wil need to open AltaMail the first time you send an email, but next time after that, emails will be sent in the background if you allow access.

Other shortcuts will be suggested as you use AltaMail. For example, when you swipe to send an email template and add some contacts, a shortcut will be created in the device Settings app - Siri settings, to repeat that process.

If you use the left side menu to open an email account folder, that action will be suggested as a shortcut in the device Settings app - Siri & Search - AltaMail settings.

You can process AltaMail shortcuts from your Lock Screen. To disable this feature, turn off "Allow on Lock Screen" in the device Settings app - Siri & Search - AltaMail settings.

Note: You will need to launch AltaMail first to create the shortcuts and it may take Siri a few minutes to add the shortcuts to the list in the device settings app. Also make sure "Use with Siri" is turned on in the device settings AltaMail section.