https://news.ycombinator.com/item?id=37127604

...didn't get any, but I found some via an unfortunate client, who was doing this via a CRM without setting any sort of domain authentication up for their sender (I do data migrations at my day job, so I see everyone's skeletons...)

tl;dr: bounce rate will be about 45-50% over time if you don't set up any sort of DKIM or SPF records, varying slightly depending on your recipients, but it's the IMPORTANT PEOPLE you can't email.

Excerpt below, <-- email domain sent to, --> email server which rejected the message.

Email Bounced | Email Server

---------------------------------------

@cbmove.com usb-smtp-inbound-1.mimecast.com.

@pattonboggs.com eu-smtp-inbound-1.mimecast.com.

@montgomerycollege.edu mx0a-0016b401.pphosted.com.

@iri.org us-smtp-inbound-1.mimecast.com.

@stemedcoalition.org us-smtp-inbound-2.mimecast.com.

@bipc.com us-smtp-inbound-1.mimecast.com.

@dickblick.com us-smtp-inbound-1.mimecast.com.

@student.american.edu mx0a-00240c01.pphosted.com.

@cbf.org us-smtp-inbound-1.mimecast.com.

@binghamt.gannett.com us-smtp-inbound-1.mimecast.com.

@hhlaw.com eu-smtp-inbound-2.mimecast.com.

@pattonboggs.com eu-smtp-inbound-1.mimecast.com.

@iri.org us-smtp-inbound-1.mimecast.com.

@tmgcustommedia.com us-smtp-inbound-1.mimecast.com.

@washington.goethe.org mx02.goethe.de.

@nbcuni.com mxb-00176a04.gslb.pphosted.com.

@jonesday.com mxb-00393202.gslb.pphosted.com.

@intelsatgeneral.com mxb-0056a401.gslb.pphosted.com.

@qga.com mxa-00173601.gslb.pphosted.com.

@wpost.com mxb-001a3c01.gslb.pphosted.com.

@nbcuni.com mx0a-00176a04.pphosted.com.

@tr.com mxb-00160c04.gslb.pphosted.com.

@arts.ri.gov mx0b-00137801.pphosted.com.

@readexpress.com mxa-001a3c01.gslb.pphosted.com.

@icloud.com mx02.mail.icloud.com.

@readexpress.com mxa-001a3c01.gslb.pphosted.com.

@nbc.com mxa-00176a04.gslb.pphosted.com.

@wellsfargoadvisors.com mxa-00004003.gslb.pphosted.com.

@american.edu mx0b-00240c01.pphosted.com.

@chron.com mxa-0018d701.gslb.pphosted.com.

@na.ko.com mxa-0037a502.gslb.pphosted.com.

@bbandt.com mxb-0058fb01.gslb.pphosted.com.

@exxonmobil.com mxa-00016305.gslb.pphosted.com.

@dcist.com mx0a-00240c01.pphosted.com.

@k12.com mxa-00678201.gslb.pphosted.com.

@stanford.edu mxb-00000d07.gslb.pphosted.com.

@ge.com mx0a-00176a02.pphosted.com.

@american.edu mx0b-00240c01.pphosted.com.

@dynetics.com mxa-00336402.gslb.gpphosted.com.

@washpost.com mxa-001a3c01.gslb.pphosted.com.

@pnc.com mxb-000ade01.gslb.pphosted.com.

@vh1staff.com mxa-00262c01.gslb.pphosted.com.

@hosthotels.com mxa-00320801.gslb.pphosted.com.

@dc.gov dc-gov.mail.protection.outlook.com.

@dc.gov dc-gov.mail.protection.outlook.com.

@arenastage.org arenastage-org.mail.protection.outlook.com.