getLeadActivity would be a suitable option.
The WSDL defines Send Email" and "Email Delivered" among others:
<xs:simpleType name="ActivityType">
<xs:restriction base="xs:string">
<xs:enumeration value="VisitWebpage"/>
<xs:enumeration value="FillOutForm"/>
<xs:enumeration value="ClickLink"/>
<xs:enumeration value="SendEmail"/>
<xs:enumeration value="EmailDelivered"/>
<xs:enumeration value="EmailBounced"/>
<xs:enumeration value="UnsubscribeEmail"/>
<xs:enumeration value="OpenEmail"/>
<xs:enumeration value="ClickEmail"/>
<xs:enumeration value="NewLead"/>
<xs:enumeration value="ChangeDataValue"/>
<xs:enumeration value="LeadAssigned"/>
<xs:enumeration value="NewSFDCOpprtnty"/>
<xs:enumeration value="Wait"/>
<xs:enumeration value="RunSubflow"/>
<xs:enumeration value="RemoveFromFlow"/>
<xs:enumeration value="PushLeadToSales"/>
<xs:enumeration value="CreateTask"/>
<xs:enumeration value="ConvertLead"/>
<xs:enumeration value="ChangeScore"/>
<xs:enumeration value="ChangeOwner"/>
<xs:enumeration value="AddToList"/>
<xs:enumeration value="RemoveFromList"/>
<xs:enumeration value="SFDCActivity"/>
<xs:enumeration value="EmailBouncedSoft"/>
<xs:enumeration value="PushLeadUpdatesToSales"/>
<xs:enumeration value="DeleteLeadFromSales"/>
<xs:enumeration value="SFDCActivityUpdated"/>
<xs:enumeration value="SFDCMergeLeads"/>
<xs:enumeration value="MergeLeads"/>
<xs:enumeration value="ResolveConflicts"/>
<xs:enumeration value="AssocWithOpprtntyInSales"/>
<xs:enumeration value="DissocFromOpprtntyInSales"/>
<xs:enumeration value="UpdateOpprtntyInSales"/>
<xs:enumeration value="DeleteLead"/>
<xs:enumeration value="SendAlert"/>
<xs:enumeration value="SendSalesEmail"/>
<xs:enumeration value="OpenSalesEmail"/>
<xs:enumeration value="ClickSalesEmail"/>
<xs:enumeration value="AddtoSFDCCampaign"/>
<xs:enumeration value="RemoveFromSFDCCampaign"/>
<xs:enumeration value="ChangeStatusInSFDCCampaign"/>
<xs:enumeration value="ReceiveSalesEmail"/>
<xs:enumeration value="InterestingMoment"/>
<xs:enumeration value="RequestCampaign"/>
<xs:enumeration value="SalesEmailBounced"/>
<xs:enumeration value="ChangeLeadPartition"/>
<xs:enumeration value="ChangeRevenueStage"/>
<xs:enumeration value="ChangeRevenueStageManually"/>
<xs:enumeration value="ComputeDataValue"/>
<xs:enumeration value="ChangeStatusInProgression"/>
<xs:enumeration value="ChangeFieldInProgram"/>
<xs:enumeration value="EnrichWithDatacom"/>
<xs:enumeration value="ChangeSegment"/>
<xs:enumeration value="ResolveRuleset"/>
<xs:enumeration value="SmartCampaignTest"/>
<xs:enumeration value="SmartCampaignTestTrigger"/>