diff --git a/lib/api/messages.js b/lib/api/messages.js
index 0a42ecb9..6712f342 100644
--- a/lib/api/messages.js
+++ b/lib/api/messages.js
@@ -2569,7 +2569,11 @@ module.exports = (db, server, messageHandler, userHandler, storageHandler) => {
 
             if (data.html && typeof data.html === 'string') {
                 let fromAddress = (data.from && data.from.address).toString() || os.hostname();
+                let cids = new Map();
                 data.html = data.html.replace(/(<img\b[^>]* src\s*=[\s"']*)(data:[^"'>\s]+)/gi, (match, prefix, dataUri) => {
+                    if (cids.has(dataUri)) {
+                        return prefix + 'cid:' + cids.get(dataUri);
+                    }
                     let cid = uuid.v4() + '-attachments@' + fromAddress.split('@').pop();
                     data.attachments.push(
                         processDataUrl({
@@ -2577,6 +2581,7 @@ module.exports = (db, server, messageHandler, userHandler, storageHandler) => {
                             cid
                         })
                     );
+                    cids.set(dataUri, cid);
                     return prefix + 'cid:' + cid;
                 });
             }
diff --git a/lib/api/submit.js b/lib/api/submit.js
index 586f4f22..9885cadf 100644
--- a/lib/api/submit.js
+++ b/lib/api/submit.js
@@ -330,7 +330,11 @@ module.exports = (db, server, messageHandler, userHandler) => {
 
                             if (data.html && typeof data.html === 'string') {
                                 let fromAddress = (data.from && data.from.address).toString() || os.hostname();
+                                let cids = new Map();
                                 data.html = data.html.replace(/(<img\b[^>]* src\s*=[\s"']*)(data:[^"'>\s]+)/gi, (match, prefix, dataUri) => {
+                                    if (cids.has(dataUri)) {
+                                        return prefix + 'cid:' + cids.get(dataUri);
+                                    }
                                     let cid = uuid.v4() + '-attachments@' + fromAddress.split('@').pop();
                                     data.attachments.push(
                                         processDataUrl({
@@ -338,6 +342,7 @@ module.exports = (db, server, messageHandler, userHandler) => {
                                             cid
                                         })
                                     );
+                                    cids.set(dataUri, cid);
                                     return prefix + 'cid:' + cid;
                                 });
                             }