diff --git a/src/pretix/base/services/mail.py b/src/pretix/base/services/mail.py
index 1ce73b47b2..0533f37bfb 100644
--- a/src/pretix/base/services/mail.py
+++ b/src/pretix/base/services/mail.py
@@ -640,13 +640,14 @@ def convert_image_to_cid(image_src, cid_id, verify_ssl=True):
             image_src = normalize_image_url(image_src)
 
             path = urlparse(image_src).path
-            guess_subtype = os.path.splitext(path)[1][1:]
+            image_type = os.path.splitext(path)[1][1:]
 
             response = requests.get(image_src, verify=verify_ssl)
             mime_image = MIMEImage(
-                response.content, _subtype=guess_subtype)
+                response.content, _subtype=image_type)
 
         mime_image.add_header('Content-ID', '<%s>' % cid_id)
+        mime_image.add_header('Content-Disposition', 'inline;\n filename="{}.{}"'.format(cid_id, image_type))
 
         return mime_image
     except:
diff --git a/src/pretix/base/templates/pretixbase/email/simple_logo.html b/src/pretix/base/templates/pretixbase/email/simple_logo.html
index 2adc87d012..072e7bf7de 100644
--- a/src/pretix/base/templates/pretixbase/email/simple_logo.html
+++ b/src/pretix/base/templates/pretixbase/email/simple_logo.html
@@ -1,12 +1,18 @@
 {% load eventurl %}
 {% load i18n %}
 {% load thumb %}
-
-<!DOCTYPE html>
-<html>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml" xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office">
 <head>
-    <meta charset="utf-8">
-    <meta name="viewport" content="width=device-width, user-scalable=false">
+<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
+<meta name="viewport" content="width=device-width, initial-scale=1.0">
+<title>{{subject}}</title>
+<!--[if gte mso 9]><xml>
+<o:OfficeDocumentSettings>
+<o:AllowPNG/>
+<o:PixelsPerInch>96</o:PixelsPerInch>
+</o:OfficeDocumentSettings>
+</xml><![endif]-->
     <style type="text/css">
         body {
             background-color: #eee;
@@ -208,21 +214,17 @@
     <table width="100%"><tr><td align="center">
     <table width="600"><tr><td align="center"
     <![endif]-->
-    <table class="layout" width="600" border="0" cellspacing="0">
+    <table class="layout" style="max-width:600px" border="0" cellspacing="0">
         {% if event.settings.logo_image %}
-            <!--[if !mso]><!-- -->
             <tr>
                 <td style="line-height: 0; {% if event.settings.logo_image_large %}padding: 0;{% endif %}" align="center" class="logo">
                     {% if event.settings.logo_image_large %}
-                        <img src="{% if event.settings.logo_image|thumb:'1170x5000'|first == '/' %}{{ site_url }}{% endif %}{{ event.settings.logo_image|thumb:'1170x5000' }}" alt="{{ event.name }}"
-                             style="height: auto; max-width: 100%;" />
+                        <img src="{% if event.settings.logo_image|thumb:'600_x5000'|first == '/' %}{{ site_url }}{% endif %}{{ event.settings.logo_image|thumb:'600_x5000' }}" alt="{{ event.name }}" style="width:100%" />
                     {% else %}
-                        <img src="{% if event.settings.logo_image|thumb:'5000x120'|first == '/' %}{{ site_url }}{% endif %}{{ event.settings.logo_image|thumb:'5000x120' }}" alt="{{ event.name }}"
-                                style="height: auto; max-width: 100%;" />
+                        <img src="{% if event.settings.logo_image|thumb:'600_x120'|first == '/' %}{{ site_url }}{% endif %}{{ event.settings.logo_image|thumb:'600_x120' }}" alt="{{ event.name }}" style="width:100%" />
                     {% endif %}
                 </td>
             </tr>
-            <!--<![endif]-->
         {% endif %}
         <tr>
             <td class="header" align="center">
diff --git a/src/pretix/helpers/thumb.py b/src/pretix/helpers/thumb.py
index 92314b8463..11b0307639 100644
--- a/src/pretix/helpers/thumb.py
+++ b/src/pretix/helpers/thumb.py
@@ -20,6 +20,7 @@
 # <https://www.gnu.org/licenses/>.
 #
 import hashlib
+import math
 from io import BytesIO
 
 from django.core.files.base import ContentFile
@@ -34,18 +35,85 @@ class ThumbnailError(Exception):
     pass
 
 
+"""
+
+# How "size" works:
+
+
+## normal resize
+
+image|thumb:"100x100" resizes the image proportionally to a maximum width and maximum height of 100px.
+I.e. an image of 200x100 will be resized to 100x50.
+An image of 40x80 will stay 40x80.
+
+
+## cropped resize with ^
+
+image|thumb:"100x100^" resizes the image proportionally to a minimum width and minimum height of 100px and then will be cropped to 100x100.
+I.e. an image of 300x200 will be resized to 150x100 and then cropped from center to 100x100.
+An image of 40x80 will stay 40x80.
+
+
+## min-size resize with _
+
+min-size-operator "_" works for width and height independently, so the following is possible:
+
+image|thumb:"100_x100" resizes the image to a maximum height of 100px (if it is lower, it does not upscale) and makes it at least 100px wide
+(if the resized image would be less than 100px wide it adds a white background to both sides to make it at least 100px wide).
+I.e. an image of 300x200 will be resized to 150x100.
+An image of 40x80 will stay 40x80 but padded with a white background to be 100x80.
+
+image|thumb:"100x100_" resizes the image to a maximum width of 100px (if it is lower, it does not upscale) and makes it at least 100px high
+(if the resized image would be less than 100px high it adds a white background to top and bottom to make it at least 100px high).
+I.e. an image of 400x200 will be resized to 100x50 and then padded from cener to be 100x100.
+An image of 40x80 will stay 40x80 but padded with a white background to be 40x100.
+
+image|thumb:"100_x100_" resizes the image proportionally to either a width or height of 100px – it takes the smaller side and resizes that to 100px,
+so the longer side will at least be 100px. So the resulting image will at least be 100px wide and at least 100px high. If the original image is bigger
+than 100x100 then no padding will occur. If the original image is smaller than 100x100, no resize will happen but padding to 100x100 will occur.
+I.e. an image of 400x200 will be resized to 200x100.
+An image of 40x80 will stay 40x80 but padded with a white background to be 100x100.
+
+"""
+
+
+def get_minsize(size):
+    if "_" not in size:
+        return (0, 0)
+    min_width = 0
+    min_height = 0
+    if "x" in size:
+        sizes = size.split('x')
+        if sizes[0].endswith("_"):
+            min_width = int(sizes[0][:-1])
+        if sizes[1].endswith("_"):
+            min_height = int(sizes[1][:-1])
+    elif size.endswith("_"):
+        min_width = int(size[:-1])
+        min_height = min_width
+    return (min_width, min_height)
+
+
 def get_sizes(size, imgsize):
     crop = False
     if size.endswith('^'):
         crop = True
         size = size[:-1]
 
+    if crop and "_" in size:
+        raise ThumbnailError('Size %s has errors: crop and minsize cannot be combined.' % size)
+
+    min_width, min_height = get_minsize(size)
+    if min_width or min_height:
+        size = size.replace("_", "")
+
     if 'x' in size:
         size = [int(p) for p in size.split('x')]
     else:
         size = [int(size), int(size)]
 
     if crop:
+        # currently crop and min-size cannot be combined
         wfactor = min(1, size[0] / imgsize[0])
         hfactor = min(1, size[1] / imgsize[1])
         if wfactor == hfactor:
@@ -61,6 +129,14 @@ def get_sizes(size, imgsize):
     else:
         wfactor = min(1, size[0] / imgsize[0])
         hfactor = min(1, size[1] / imgsize[1])
+        if min_width and min_height:
+            wfactor = max(wfactor, hfactor)
+            hfactor = wfactor
+        elif min_width:
+            wfactor = hfactor
+        elif min_height:
+            hfactor = wfactor
+
         if wfactor == hfactor:
             return (int(imgsize[0] * hfactor), int(imgsize[1] * wfactor)), None
         elif wfactor < hfactor:
@@ -69,6 +145,32 @@ def get_sizes(size, imgsize):
             return (int(imgsize[0] * hfactor), size[1]), None
 
 
+def resize_image(image, size):
+    # before we calc thumbnail, we need to check and apply EXIF-orientation
+    image = ImageOps.exif_transpose(image)
+
+    new_size, crop = get_sizes(size, image.size)
+    image = image.resize(new_size, resample=LANCZOS)
+    if crop:
+        image = image.crop(crop)
+
+    min_width, min_height = get_minsize(size)
+
+    if min_width > new_size[0] or min_height > new_size[1]:
+        padding = math.ceil(max(min_width - new_size[0], min_height - new_size[1]) / 2)
+        image = image.convert('RGB')
+        image = ImageOps.expand(image, border=padding, fill="white")
+
+        new_width = max(min_width, new_size[0])
+        new_height = max(min_height, new_size[1])
+        new_x = (image.width - new_width) // 2
+        new_y = (image.height - new_height) // 2
+
+        image = image.crop((new_x, new_y, new_x + new_width, new_y + new_height))
+
+    return image
+
+
 def create_thumbnail(sourcename, size):
     source = default_storage.open(sourcename)
     image = Image.open(BytesIO(source.read()))
@@ -77,13 +179,7 @@ def create_thumbnail(sourcename, size):
     except:
         raise ThumbnailError('Could not load image')
 
-    # before we calc thumbnail, we need to check and apply EXIF-orientation
-    image = ImageOps.exif_transpose(image)
-
-    scale, crop = get_sizes(size, image.size)
-    image = image.resize(scale, resample=LANCZOS)
-    if crop:
-        image = image.crop(crop)
+    image = resize_image(image, size)
 
     if source.name.endswith('.jpg') or source.name.endswith('.jpeg'):
         # Yields better file sizes for photos
diff --git a/src/tests/helpers/test_thumb.py b/src/tests/helpers/test_thumb.py
new file mode 100644
index 0000000000..91e72986bf
--- /dev/null
+++ b/src/tests/helpers/test_thumb.py
@@ -0,0 +1,116 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+from PIL import Image
+
+from pretix.helpers.thumb import resize_image
+
+
+def test_no_resize():
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "100x100")
+    width, height = img.size
+    assert width == 40
+    assert height == 20
+
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "100x100^")
+    width, height = img.size
+    assert width == 40
+    assert height == 20
+
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "10_x20")
+    width, height = img.size
+    assert width == 40
+    assert height == 20
+
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "40x10_")
+    width, height = img.size
+    assert width == 40
+    assert height == 20
+
+
+def test_resize():
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "10x10")
+    width, height = img.size
+    assert width == 10
+    assert height == 5
+
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "100x10")
+    width, height = img.size
+    assert width == 20
+    assert height == 10
+
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "10x100")
+    width, height = img.size
+    assert width == 10
+    assert height == 5
+
+
+def test_crop():
+    img = Image.new('RGB', (40, 20))
+    img = resize_image(img, "10x10^")
+    width, height = img.size
+    assert width == 10
+    assert height == 10
+
+
+def test_minsize():
+    img = Image.new('RGB', (60, 20))
+    img = resize_image(img, "10_x10")
+    width, height = img.size
+    assert width == 30
+    assert height == 10
+
+    img = Image.new('RGB', (10, 20))
+    img = resize_image(img, "10_x10")
+    width, height = img.size
+    assert width == 10
+    assert height == 10
+
+    img = Image.new('RGB', (60, 20))
+    img = resize_image(img, "10x10_")
+    width, height = img.size
+    assert width == 10
+    assert height == 10
+
+    img = Image.new('RGB', (20, 60))
+    img = resize_image(img, "10x10_")
+    width, height = img.size
+    assert width == 10
+    assert height == 30
+
+    img = Image.new('RGB', (20, 60))
+    img = resize_image(img, "10_x10_")
+    width, height = img.size
+    assert width == 10
+    assert height == 30
+
+    img = Image.new('RGB', (20, 60))
+    img = resize_image(img, "100_x100_")
+    width, height = img.size
+    assert width == 100
+    assert height == 100
