Skip emails with incorrect email when export ics file (#5190)

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#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

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- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

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* #<issue>

#### Test Plan

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- [ ] 💪 Manual
- [x] ⚡ Unit test
- [ ] 💚 E2E

src/internal/converters/ics/ics.go

@@ -5,6 +5,7 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"net/mail"
 	"strings"
 	"time"
 	"unicode"
@@ -279,6 +280,12 @@ func isASCII(s string) bool {
 	return true
 }
 
+// Checks if a given string is a valid email address
+func isEmail(em string) bool {
+	_, err := mail.ParseAddress(em)
+	return err == nil
+}
+
 func updateEventProperties(ctx context.Context, event models.Eventable, iCalEvent *ics.VEvent) error {
 	// CREATED - https://www.rfc-editor.org/rfc/rfc5545#section-3.8.7.1
 	created := event.GetCreatedDateTime()
@@ -481,8 +488,21 @@ func updateEventProperties(ctx context.Context, event models.Eventable, iCalEven
 			}
 		}
 
+		// It is possible that we get non email items like the below
+		// one which is an internal representation of the user in the
+		// Exchange system. While we can technically output this as an
+		// attendee, it is not useful plus other downstream tools like
+		// ones to use PST can choke on this.
+		// /o=ExchangeLabs/ou=ExchangeAdministrative Group(FY...LT)/cn=Recipients/cn=883...4a-John Doe
 		addr := ptr.Val(attendee.GetEmailAddress().GetAddress())
+		if isEmail(addr) {
 			iCalEvent.AddAttendee(addr, props...)
+		} else {
+			logger.Ctx(ctx).
+				With("attendee_email", addr).
+				With("attendee_name", name).
+				Info("skipping non email attendee from ics export")
+		}
 	}
 
 	// LOCATION - https://www.rfc-editor.org/rfc/rfc5545#section-3.8.1.7

src/internal/converters/ics/ics_test.go

@@ -908,6 +908,17 @@ func (suite *ICSUnitSuite) TestAttendees() {
 					"attendee")
 			},
 		},
+		{
+			name: "attendee with internal exchange representation for email",
+			att: [][]string{{
+				"/o=ExchangeLabs/ou=ExchangeAdministrative Group(FY...LT)/cn=Recipients/cn=883...4a-John Doe",
+				"required",
+				"declined",
+			}},
+			check: func(out string) {
+				assert.NotContains(t, out, "ATTENDEE")
+			},
+		},
 		{
 			name: "multiple attendees",
 			att: [][]string{