diff --git a/Olive.Email/Email.Sending/MailMessageCreator.cs b/Olive.Email/Email.Sending/MailMessageCreator.cs
index 9241eb7cf..275fc4e49 100644
--- a/Olive.Email/Email.Sending/MailMessageCreator.cs
+++ b/Olive.Email/Email.Sending/MailMessageCreator.cs
@@ -1,121 +1,127 @@
-using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Configuration;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net.Mail;
 using System.Net.Mime;
 using System.Threading.Tasks;
 
-namespace Olive.Email
+namespace Olive.Email;
+
+/// <summary>
+/// Creates <see cref="MailMessage"/> instances based on an <see cref="IEmailMessage"/>.
+/// </summary>
+public interface IMailMessageCreator
+{
+    Task<MailMessage> Create(IEmailMessage message);
+}
+
+/// <summary>
+/// Default implementation of <see cref="IMailMessageCreator"/>.
+/// </summary>
+public sealed class MailMessageCreator : IMailMessageCreator
 {
-    public interface IMailMessageCreator
+    private readonly EmailConfiguration _config;
+    private readonly IEmailAttachmentSerializer _attachmentSerializer;
+
+    public MailMessageCreator(IConfiguration config, IEmailAttachmentSerializer attachmentSerializer)
     {
-        Task<MailMessage> Create(IEmailMessage message);
+        ArgumentNullException.ThrowIfNull(config);
+        _config = config.GetSection("Email").Get<EmailConfiguration>() ?? new EmailConfiguration();
+        _attachmentSerializer = attachmentSerializer ?? throw new ArgumentNullException(nameof(attachmentSerializer));
     }
 
-    class MailMessageCreator : IMailMessageCreator
+    public async Task<MailMessage> Create(IEmailMessage message)
     {
-        EmailConfiguration Config;
+        ArgumentNullException.ThrowIfNull(message);
 
-        public MailMessageCreator(IConfiguration config, IEmailAttachmentSerializer attachmentSerializer)
+        var result = new MailMessage
         {
-            Config = config.GetSection("Email").Get<EmailConfiguration>();
-            AttachmentSerializer = attachmentSerializer;
-        }
+            Subject = message.Subject.Or("[NO SUBJECT]").Remove("\r", "\n"),
+            Body = message.Body,
+            From = CreateFrom(message)
+        };
 
-        public IEmailAttachmentSerializer AttachmentSerializer { get; }
+        result.Headers.Add(Constants.EMAIL_MESSAGE_ID_HEADER_KEY, message.GetId().ToString());
 
-        public async Task<MailMessage> Create(IEmailMessage message)
-        {
-            var result = new MailMessage
-            {
-                Subject = message.Subject.Or("[NO SUBJECT]").Remove("\r", "\n"),
-                Body = message.Body,
-                From = CreateFrom(message)
-            };
+        foreach (var recipient in GetEffectiveRecipients(message.To))
+            result.To.Add(recipient);
 
-            result.Headers
-                .Add(Constants.EMAIL_MESSAGE_ID_HEADER_KEY, message.GetId().ToString());
+        foreach (var recipient in GetEffectiveRecipients(message.Cc + _config.AutoAddCc.WithPrefix(",")))
+            result.CC.Add(recipient);
 
-            GetEffectiveRecipients(message.To).Do(x => result.To.Add(x));
-            GetEffectiveRecipients(message.Cc + Config.AutoAddCc.WithPrefix(",")).Do(x => result.CC.Add(x));
-            GetEffectiveRecipients(message.Bcc + Config.AutoAddBcc.WithPrefix(",")).Do(x => result.Bcc.Add(x));
+        foreach (var recipient in GetEffectiveRecipients(message.Bcc + _config.AutoAddBcc.WithPrefix(",")))
+            result.Bcc.Add(recipient);
 
-            result.ReplyToList.Add(CreateReplyTo(message));
+        result.ReplyToList.Add(CreateReplyTo(message));
 
-            result.AlternateViews.AddRange(GetBodyViews(message));
-            result.Attachments.AddRange(await AttachmentSerializer.Extract(message));
+        result.AlternateViews.AddRange(GetBodyViews(message));
+        result.Attachments.AddRange(await _attachmentSerializer.Extract(message));
 
-            return result;
-        }
+        return result;
+    }
 
-        MailAddress CreateFrom(IEmailMessage message)
-        {
-            var address = message.FromAddress.Or(Config.From?.Address);
-            var name = message.FromName.Or(Config.From?.Name);
-            return new MailAddress(address, name);
-        }
+    private MailAddress CreateFrom(IEmailMessage message) =>
+        new(message.FromAddress.Or(_config.From?.Address),
+            message.FromName.Or(_config.From?.Name));
 
-        MailAddress CreateReplyTo(IEmailMessage message)
-        {
-            var address = message.ReplyToAddress
-                .Or(Config.ReplyTo?.Address)
-                .Or(message.FromAddress)
-                .Or(Config.From?.Address);
+    private MailAddress CreateReplyTo(IEmailMessage message)
+    {
+        var address = message.ReplyToAddress
+            .Or(_config.ReplyTo?.Address)
+            .Or(message.FromAddress)
+            .Or(_config.From?.Address);
 
-            var name = message.ReplyToName
-                .Or(Config.ReplyTo?.Name)
-                .Or(message.FromName)
-                .Or(Config.From?.Name);
+        var name = message.ReplyToName
+            .Or(_config.ReplyTo?.Name)
+            .Or(message.FromName)
+            .Or(_config.From?.Name);
 
-            return new MailAddress(address, name);
-        }
+        return new MailAddress(address, name);
+    }
 
-        string[] GetEffectiveRecipients(string to)
-        {
-            return to.OrEmpty().Split(',').Trim().Where(x => CanSendTo(x)).ToArray();
-        }
+    private IEnumerable<string> GetEffectiveRecipients(string? to) =>
+        to.OrEmpty().Split(',').Trim().Where(CanSendTo);
 
-        bool CanSendTo(string recipientAddress)
-        {
-            var permittedDomains = Config.Permitted.Domains.ToLowerOrEmpty().Or("geeks.ltd.uk|uat.co");
-            if (permittedDomains == "*") return true;
+    private bool CanSendTo(string recipientAddress)
+    {
+        var permittedDomains = _config.Permitted.Domains.ToLowerOrEmpty().Or("geeks.ltd.uk|uat.co");
+        if (permittedDomains == "*") return true;
 
-            if (permittedDomains.Split('|').Trim().Any(d => recipientAddress.TrimEnd(">").EndsWith("@" + d)))
-                return true;
+        if (permittedDomains.Split('|').Trim().Any(d => recipientAddress.TrimEnd(">").EndsWith("@" + d)))
+            return true;
 
-            var addresses = Config.Permitted.Addresses.ToLowerOrEmpty().Split('|').Trim().ToArray();
+        var addresses = _config.Permitted.Addresses.ToLowerOrEmpty().Split('|').Trim().ToArray();
 
-            return addresses.Any() && new MailAddress(recipientAddress).Address.IsAnyOf(addresses);
-        }
+        return addresses.Any() && new MailAddress(recipientAddress).Address.IsAnyOf(addresses);
+    }
 
-        IEnumerable<AlternateView> GetBodyViews(IEmailMessage message)
-        {
-            yield return AlternateView.CreateAlternateViewFromString(
-                message.Body.RemoveHtmlTags(),
+    private IEnumerable<AlternateView> GetBodyViews(IEmailMessage message)
+    {
+        yield return AlternateView.CreateAlternateViewFromString(
+            message.Body.RemoveHtmlTags(),
             new ContentType("text/plain; charset=UTF-8"));
 
-            if (message.Html)
-            {
-                var htmlView = AlternateView.CreateAlternateViewFromString(
-                    message.Body, new ContentType("text/html; charset=UTF-8"));
-
-                htmlView.LinkedResources.AddRange(AttachmentSerializer.GetLinkedResources(message));
-                yield return htmlView;
-            }
+        if (message.Html)
+        {
+            var htmlView = AlternateView.CreateAlternateViewFromString(
+                message.Body,
+                new ContentType("text/html; charset=UTF-8"));
 
-            if (message.VCalendarView.HasValue())
-            {
-                var calendarType = new ContentType("text/calendar");
-                calendarType.Parameters.Add("method", "REQUEST");
-                calendarType.Parameters.Add("name", "meeting.ics");
+            htmlView.LinkedResources.AddRange(_attachmentSerializer.GetLinkedResources(message));
+            yield return htmlView;
+        }
 
-                var calendarView = AlternateView
-                    .CreateAlternateViewFromString(message.VCalendarView, calendarType);
+        if (message.VCalendarView.HasValue())
+        {
+            var calendarType = new ContentType("text/calendar");
+            calendarType.Parameters.Add("method", "REQUEST");
+            calendarType.Parameters.Add("name", "meeting.ics");
 
-                calendarView.TransferEncoding = TransferEncoding.SevenBit;
+            var calendarView = AlternateView.CreateAlternateViewFromString(message.VCalendarView, calendarType);
+            calendarView.TransferEncoding = TransferEncoding.SevenBit;
 
-                yield return calendarView;
-            }
+            yield return calendarView;
         }
     }
-}
\ No newline at end of file
+}
+