Transaction fails when mail is sent in the same transaction as a new version is saved

[ghost]

I'm using CMFEditions 2.2.20 in Plone 5.0.5. I have an event listener on content (that uses the plone.app.versioningbehavior.behaviors.IVersionable behavior) that sends automatic email. However this fails with the following error.

Traceback (innermost last):

    Module ZPublisher.Publish, line 138, in publish
    Module ZPublisher.mapply, line 77, in mapply
    Module ZPublisher.Publish, line 48, in call_object
    Module plone.z3cform.layout, line 66, in __call__
    Module plone.z3cform.layout, line 50, in update
    Module plone.dexterity.browser.edit, line 58, in update
    Module plone.z3cform.fieldsets.extensible, line 59, in update
    Module plone.z3cform.patch, line 30, in GroupForm_update
    Module z3c.form.group, line 145, in update
    Module plone.app.z3cform.csrf, line 21, in execute
    Module z3c.form.action, line 98, in execute
    Module z3c.form.button, line 315, in __call__
    Module z3c.form.button, line 170, in __call__
    Module plone.dexterity.browser.edit, line 30, in handleApply
    Module z3c.form.group, line 126, in applyChanges
    Module zope.event, line 31, in notify
    Module zope.component.event, line 24, in dispatch
    Module zope.component._api, line 136, in subscribers
    Module zope.component.registry, line 321, in subscribers
    Module zope.interface.adapter, line 585, in subscribers
    Module zope.component.event, line 32, in objectEventNotify
    Module zope.component._api, line 136, in subscribers
    Module zope.component.registry, line 321, in subscribers
    Module zope.interface.adapter, line 585, in subscribers
    Module plone.app.versioningbehavior.subscribers, line 62, in create_version_on_save
    Module Products.CMFEditions.CopyModifyMergeRepositoryTool, line 305, in save
    Module Products.CMFEditions.CopyModifyMergeRepositoryTool, line 450, in _recursiveSave
    Module Products.CMFEditions.ArchivistTool, line 265, in prepare
    Module Products.CMFEditions.ModifierRegistryTool, line 143, in getReferencedAttributes
    Module plone.app.versioningbehavior.modifiers, line 114, in getReferencedAttributes
    Module Products.CMFEditions.CopyModifyMergeRepositoryTool, line 366, in retrieve
    Module Products.CMFEditions.CopyModifyMergeRepositoryTool, line 500, in _retrieve
    Module transaction._transaction, line 705, in rollback
    Module transaction._transaction, line 702, in rollback
    Module transaction._transaction, line 723, in rollback

TypeError: ('Savepoints unsupported', <zope.sendmail.delivery.MailDataManager object at 0x00000000170D6160>)

I can confirm that this is the cause because it works if I remove the dexterity behavior I get the email and no error (and no versioning) or if comment out the line that sends the email I get proper versioning and no behavior. I don't understand the low level transaction module too well but it seems like sending an email shouldn't be something that causes a db conflict.

The problem looks like it might be related to a fix waaay back in the day here My problem looks very similar to https://github.com/plone/Products.CMFEditions/blob/master/CHANGES.rst#205---2011-02-25 but I am not enough of an expert to know if that is a red herring.

[terapyon]

I got same error on Plone 5.1rc2. I think the problem related zope.sendmail. I want to know how to fix or any workaround.